Swimming timing improvement help

Question: I'm 16 yrs old.my freestyle 100m timing is 1.05.14 is it possible for me to get my timing down to 54 secs before April 2018
Comment: Youre asking to knock off about 10s time in less than a year. It is doable, but it is going to be really, really hard. What is your age? how many times do you swim? etc.
Comment: How on earth are we supposed to know that? We know literally nothing about you.
Comment: While not impossible, it will be hard going. You need to improve your strength, conditioning, and stroke all together. But, take it one step at a time. Be sure to race often, trying different strategies.
Comment: I don't see the hate for this question. If the guy asked "Can I get my bench from 135lbs to 225lbs in a year's time?" He'd probably get a solid answer.
Comment: The hate for this question should be obvious. Without quite a bit more information, we can only give advice like the two responses below which are _extremely_ generic training and racing advice.

If OP had said, "I only swim twice a week 3000m," then we could suggest an increased training regimen. If OP stated that they are an active swimmer, then I might interpret his question more as frustration as in, "I put all these hours in to swimming and my peers are 10s faster than me, what am I doing wrong?"

Furthermore, OP never followed up on any of it.
Answer: As it is stated, it's not really possible to say for sure if you can get your 100m freestyle time down to 54 seconds in a year. 10 seconds in a year is a very big jump, but there are some things to look at that may help.

Form - Freestyle sprinting is all about efficiency and form. If your form is whonky or you are not as streamlined as you could be, then you could be costing yourself valuable time that is basically free for drills. This can really only be assessed by an on the deck instructor that can look at your form. The best ones will also utilize above and underwater video from multiple angles.
Strength/Conditioning - Dryland drills are just as important as your workout routine. Flexibility in your ankles/calves and shoulders will allow greater range of motion and efficiency (See #1).
Threshold/Interval work - No two ways about it, you have to spend a lot of time in the pool making it hurt. Interval is short distance, long rest done at above race pace. Threshold work is also short to medium distance, done on shorter rest, at about 80-90% (Depending) of race pace. Along with that, you need the usual form drills, distance conditioning, multiple stroke work, etc.
Nutrition - Critical. You have to be properly fueled, and have quality food at that. If you are doing huge volume, then you may need to take some shortcuts with high calorie dense foods, but try to make sure that a majority of your calories are serving a purpose and not just more.
Rest - Also critical. You can't perform good workouts or races when you are tired. There will be days when you feel awesome, days when you feel like dog meat. Take advantage of the great days and push extra, and relax and/or skip days when you don't feel good.

There are a lot of other little details, like shaving, tapering, race preparation, start practice, etc., but that you really need to have a coach help you with planning and details.
Answer: Hard to say without knowing your physical attributes, your technique or training program....But shaving 10s off in 9 months is a big task for anybody.
I can only make these suggestions based on my own experience - training (lots of it), a good coach, and attitude/perseverance.
Sleep and nutrition helps too.
I competed at state and national level in my youth, and my best at 16 was 54.9s for the 100m free. I'm not a tall bloke - 175cm, weighed about 55-60kgs at 16, so not a big bloke either.
I trained about 8-9 times a week - both morning and night, both at club and school. Some sessions would hit the 10km mark. Club races on the weekend.  My training consisted of lots of sprint work, heart rate sets, some distance/endurance work, and dry-land strength work. And a good taper period before a state/national meet.
The 50m and 100m are explosive movements - you'll need to improve your technique, your stroke efficiency (distance per stroke), but probably more importantly your kick (both power and endurance).  It's hard to perfect form in an all-out sprint, but for me, the breakdown was this:

The dive - Sets you up for a good sprint.  Work on getting speed and distance off the block, and your streamlining/speed under the water up to the maximum legal distance. Not sure what it is these days, but when I completed it was something like 15m underwater...Improving your butterfly/dolphin kick here is important - remember that you travel faster under the surface than you do on it. DO NOT take a breath as you surface - you'll drastically lose speed.
The first lap - explosive, but pace yourself. This is where you'll focus on technique - You'll need every bit of energy for an all effort on the last lap. As many strokes as possible before taking the first breath, and then as many as possible in between breaths - a minimum of 4 strokes/breath was my aim.  Try to get as far as possible with each stroke. And kick - use those legs.
The Turn - Fast and efficient, and set up for getting good power off the wall for fast underwater movement up to the legal distance - same as the dive.  Again, do not take a breath right before the turn, nor as you surface coming out of the turn.
The last leg - all out effort.  No time to focus on technique (nor your competitors) here, it's all or nothing.  Again, as many strokes as you can between breaths, and get those legs moving.
Hitting the wall. Literally. Power through your last few strokes and finish with an almighty reach to punch through that wall.  Don't back off - let the wall stop you.

And one last note - I always shaved down on the morning of the meet. Whole body.
Those shaving cuts serve as real motivators to get to the finish!

Swimming timing improvement help


How do I accurately select half of a symmetrical mesh?

Question: I have this mesh that is probably nearly 100% symmetrical on both sides. I want to easily select half of the mesh, in order to hide it to have easy access to its inside. My object is directly aligned with the origin, so would there be like a Hot-key to be able to select any parts of a mesh in one side of the axis?
Answer: You can select everything relative to the last selected (active) vertex.

Select the middle vertex
Access the menu: Select -> Side of Active.(Which has options regarding which side/axis).
Answer: In wireframe view enable Ortho view (Numpad 5)
Unselect everything ( A)
Use Border Select (B) to draw a box around the vertices you want to select.

Hide the vertices by pressing H.
Remember to press AltH to un-hide when you are done!
Comment: While this is great for low-poly meshes, I have a really dense mesh which doesn't make selection as 100% accurate or clean as I would like.


Database to store arrays of integers and bitset in

Question: I am building a small image search engine that uses image descriptors that are both binary numbers and integer valued (numpy) arrays which are both the 'keys' which should both form the basis for an inverted file like approach. The value is simply the image name/identifier they originated from.
I am looking for a database / caching solution with a python interface that will allow me to quickly search for these keys and not have me worry about memory and disc management.
Answer: Arrays in Python are instances of the class array
If you mean "list", use preferably the term 'list'
If I understand correctly, you use a data structure having integers as keys, and binary numbers as values: in Python it's a dictionary
If you want to record this data structure in a file, use the module cPickle
.
update
there was a 'hello, welcome' at the beginning of my post... I rewrite it here
Comment: I edited a bit for clarity. I specifically do not want to use my own file for storage.


Difference between +x and ./

Question: Are there any actual differences between running a script with
[sudo] sh ./

Difference between +x and ./


How do you insulate your pipes to protect against freezing?

Question: So, my pipes froze in my house today, and it made me realize that I should better insulate them for the rare days that it gets in the teens here... What should I do to insulate them?
Answer: Something like this foam pipe insulation should do the job:

Source - UK site, but you should be able to source this in the States.
It's split down the length so you can wrap it round existing pipes. It's flexible and easily cut so you can do corners and bends too. You might need to tape it a regular intervals to keep the insulation in place if there's not a lot of room between the pipes and any walls/beams.
Comment: I use foam insulation like that and it should be noted that you need to make sure water cant seep in. If you have a path for water to get in, you have a nice conductive path for heat to get out. The insulation is still better than none at all but if it is cold enough and wet enough it can still be a pain.
Comment: Silly question, but for pipes that are bracketed to the wall, how do you keep them on? Duct tape? Glue?
Comment: @SeanDuggan Not sure what you mean, but you can cut the insulation to the distance between the brackets. Or do  you mean that there's little/no gap between the pipe and the wall?
Comment: A little bit of both. I tried just sliding it over as best I could, but it keeps popping back off.
Answer: As well as straight lengths of pipe insulation, you can also get insulated pipe wrap, which may be easier or harder to use in some situations. one advantage is that it can be used to wrap multiple (same temperature) pipes at the same time.
Answer: If the pipes are not inside of walls, like in an unfinished basement, one option is to use wrap-on pipe heating cables. They're a bit like an extension cord that you wrap around a pipe and plugin. It radiates. It can have a thermostat to turn on at a certain temp.
Comment: Some of them have a little light on them so you can tell at a glance that they're on, which is quite reassuring.
Comment: ...right up until the power goes out.  I'd save that as a last resort if passive methods aren't good enough.


Import mysql tables from one database dump into an independent database

Question: This seems like a fairly obvious bit of functionality that mysql command would include, but I can't seem to pin it down anywhere on the man page for it.  My question is this: given a database dump generated by mysqldump ... <databasename> > file.sql can you import all of the tables (and just the tables) included into a separate database?  I'm probably missing something obvious, I'm a bit of a noob, sorry.
Answer: Sure:
mysql -uusername -ppassword -hdbserver someotherdatabasename < file.sql
There might be some confusion because you use mysqldump to extract, but mysql to load.  Note that what comes out of the mysqldump command are SQL statements, so you can just direct that into the commandline mysql command.  Or am I misunderstanding your question?
Comment: I needed to remove a table from the dumped file first, so I just went into the dump file and removed the appropriate table and removed that first, then did the import as you specified.  Thanks for the tip cjc.  Cheers.
Answer: If you want just the table structure to be dumped, create your dump file using mysqldump -d .... That will exclude all data from your dump, leaving just the structure and any other details you might choose to include (triggers, etc.).
If you're stuck with the dump you've got, then you can use some text parsing to find your way about. Except for quoted lines that have a line return in them, passing your file through grep -v '^INSERT' will remove any lines that are placing data into your database.
If you do have more complicated entries where there are line returns in the text, you'll have to use further regex filters to parse out lines that aren't valid SQL commands.
Comment: Instead of parsing through it with regexes, I would just import the whole thing someplace temporary, then dump it out with the `-d` option.  Safer.
Comment: @cjc If you can afford to load the whole whole thing, then yes that's safer. Load, truncate, dump again... or even skip the truncation and use `-d`. I've worked with some **big** dumps where loading the full dump is not practical. To that end, I've also created some state machine perl scripts that turn dumping on / off from a file for select tables only.


Photoshop CS4 Actions problem

Question: I have quite a few images with different titles in PDF format and want to turn them into jpgs. I record the action but when applying it, all the files will have the same title as the one when I recorded the action. I'm sure there must be some preference setting. I can perform this action perfectly in CS. Please help
Answer: On a mac you might want to just use automator for this:

Photoshop CS4 Actions problem


「だいたい」と「くらい」の違い

Question: I've searched online and all that I can find is that they both mean "around". What do they mean? When do you use だいたい? When do you use くらい?
Answer: What dictionary are you using?  Does the dictionary not list other English translations?
I have two suggestions:

Look at all the translations all together.  That will often give you a general sense of what the word means.
Look at the example sentences.  Online dictionaries like jisho.org provide example sentences that illustrate how the words are used.

I have a preference for the written word and trust online sources less than what's printed.  If you have a print dictionary, the two points above will not likely lead you astray.  The editors of print dictionaries (particularly the dictionaries for native Japanese speakers) put considerable time into writing up the entries and providing illustrative example sentences of usage.  The thing is you don't have to be a native speaker to find these dictionaries useful.  I used these dictionaries from the get-go when I barely knew much Japanese at all.
Online dictionaries sometime cull their example sentences in ways that are less than helpful.  Generally, it appears, no thought was put into the example sentences (after all that's resource intense work). That said, jisho seems to do generally a good job.
Of course, if you look up くらい you'll discover it has quite a variety of meanings:  from dark to position/rank to approximately.  As always with Japanese, context will drive this.
Also, keep in mind that about itself has very broad applications and its meaning in English is not very precise but more or less determined by context.
Look at these entries in jisho and their associated example sentences:

くらい and a collection of example sentences

だいたい and  a collection of example sentences

「だいたい」と「くらい」の違い


Whirlpool Duet front-loading washer won't spin

Question: I have a Whirlpool Duet front-loading washer.  Sometimes it stops and won't spin then displays code F02.  Usually turning it off for an hour and restarting solves the problem but not tonight.  When I try to restart it, it makes a grumbling sound for a while then gives up and beeps/displays the code.  Previously I opened it up and there were no obvious problems.  I checked the drain pump trap and there was nothing in it.  There isn't much in it so I don't think overloading is the problem.
Comment: Update:  I didn't have time to work on this one myself so I called in an expert.  The impeller on the pump is broken.  New one on order.  It turns out that the washer won't spin when it can't drain.  That's what threw me off.
Answer: The pump is bad or you use too much soap. Run a load without soap. If a load of clean clothes makes suds in the washer, you definitely use too much soap.
The pump can't pump suds -shopyourway.com
Of course it could be a senor malfunctioning somewhere...
Comment: I don't think it's the soap.  There aren't any suds in it now.  I can't re-run it.  When I try it just grumbles then beeps.


What should I do if I can't get a copy of original transcript from the institute?

Question: I saw an offer for a Ph.D. position in US where they asked for original transcript which directly should be sent from the home institute. When I asked my institute, they said they don't have these kind of options. In this case what can I do? Should I write the programme co-ordinator?
Comment: That's tough, my mother-in-law had similar problems.  In her case she had attended a communist-era Soviet school that had nothing for her.  Have you tried asking the school to send what they can for you?  If you've tried that, call the department at the school of interest and ask what they suggest.
Comment: Yeah this seems like something you need to work out with your home institution; if they will not send it via mail, perhaps they can send it via fax or electronically? If so you could ask the program you are applying to if that would suffice.
Comment: official transcripts from all previous colleges / universities attended
Comment: They said if u need any seal,any letter,the university is ready to give it.But they never send anything via mail. May be I can write the supervisor again regarding this matter.
Answer: Yes, you should write the coordinator at the program you're applying to, explain the situation and ask for permission to submit a copy of your transcript (I assume you have one?) rather than an original. To remove doubt that you are playing some funny games, offer to append a notarized statement from you attesting to the authenticity of the document, and say you'd be willing to take any other reasonable measures they would like you to take to accept the document.
Since the school is in the U.S., I'm guessing they'll be reasonable.


How to call smart contract methods without abi?

Question: I need to call a smart contract from python, but it is not verified. Since this is not my contract, I cannot verify it. How to call the smart contract methods through python in this case?
Smart contract: https://explorer.dogechain.dog/address/0x4aE2bD0666c76C7f39311b9B3e39b53C8D7C43Ea/contracts#address-tabs
Comment: You'll need the contract's ABI.
Answer: If you can work out what is being sent you can recraft it and send the raw data with a normal transaction, just steal the function sig and pad your values correctly.
Example raw transfer:

In your case you can see they have exactInputSingle(), so you can guess that and other similar Uniswap functions are also in the multicalls, search signatures in the 4byte directory and break the calls down:

You could also write your own abi for that function or take from a contract with the same function and arguments. Look up sig/arguments on 4byte directory.
Have done this with an unverified farming contract that was just passing pid, amount and address to withdraw.
Something like:


ODE solution as power series

Question: Consider the equation
$$(x+3)y''+2y'-4(x+3)y=0.$$
I was trying to solve it by finding the solution in the form of power series. However, I stuck while trying to find any regularity in the coefficients, while Wolfram Alpha provides a pretty much nice answer. Could you please point out the direction?
Answer: There is a life hack just for you: solve the thing with Wolfram, see how it could be simplified, then solve it the way you were supposed to. What if we switch to $u(x)=(x+3)\cdot y(x)$ and look for that in the form of power series?
Comment: This is a really helpful observation. I must admit I could not spot such a trick!
Answer: You could certainly use power series, but I use the expansion about the point $x=-3$ rather than $x=0$ (since you have those $(x+3)$ terms). Alternatively, let $z(x)=(x+3)y(x)$, so $z'=(x+3)y'+y$ and $z''=(x+3)y''+2y'$. You can then find a fairly simple ODE for $z$ and solve it however you like.

ODE solution as power series


Why is it not a good idea to dynamically create a lot of symbols in ruby (for versions before 2.2)?

Question: What is the function of symbol in ruby? what's difference between string and symbol?
Why is it not a good idea to dynamically create a lot of symbols?
Comment: Were you working thru the [EdgeCase Ruby koans](http://rubykoans.com/) too?
Comment: @ack_inc because symbols are garbage collected since Ruby 2.2 while before they lived in memory forever. So creating a lot of them has a drastically different (smaller) impact from Ruby 2.2 onwards.
Comment: Could someone update this question to specify **Ruby 2.1** or **Ruby versions before 2.2**
Comment: @dewet: could you also mention why?
Answer: Symbols are like strings but they are immutable - they can't be modified.
They are only put into memory once, making them very efficient to use for things like keys in hashes but they stay in memory until the program exits. This makes them a memory hog if you misuse them.
If you dynamically create lots of symbols, you are allocating a lot of memory that can't be freed until your program ends (edit: this is no longer the case since Ruby 2.2). You should only dynamically create symbols (using string.to_sym) if you know you will:

need to repeatedly access the symbol
not need to modify them

As I said earlier, they are useful for things like hashes - where you care more about the identity of the variable than its value. Symbols, when correctly used, are a readable and efficient way to pass around identity.
I will explain what I mean about the immutability of symbols RE your comment.
Strings are like arrays; they can be modified in place:
12:17:44 ~$ irb
irb(main):001:0> string = "Hello World!"
=> "Hello World!"
irb(main):002:0> string[5] = 'z'
=> "z"
irb(main):003:0> string
=> "HellozWorld!"
irb(main):004:0>

Symbols are more like numbers; they can't be edited in place:
irb(main):011:0> symbol = :Hello_World
=> :Hello_World
irb(main):012:0> symbol[5] = 'z'
NoMethodError: undefined method `[]=' for :Hello_World:Symbol
    from (irb):12
    from :0

Comment: Could someone update this question to specify **Ruby 2.1** or **Ruby versions before 2.2**
Comment: If a symbol is not dynamically created, then it can not be modified? can you give me a example?
Answer: A symbol is the same object and the same allocation of memory no matter where it is used:
>> :hello.object_id
=> 331068
>> a = :hello
=> :hello
>> a.object_id
=> 331068
>> b = :hello
=> :hello
>> b.object_id
=> 331068
>> a = "hello"
=> "hello"
>> a.object_id
=> 2149256980
>> b = "hello"
=> "hello"
>> b.object_id
=> 2149235120
>> b = "hell" + "o"

Two strings which are 'the same' in that they contain the same characters may not reference the same memory, which can be inefficient if you're using strings for, say, hashes.
So, symbols can be useful for reducing memory overhead. However - they are a memory leak waiting to happen, because symbols cannot be garbage collected once created. Creating thousands and thousands of symbols would allocate the memory and not be recoverable. Yikes!
Comment: You can't garbage collect symbols as far as I know. You can start garbage collection at any time with `GC.start`. Here's a good article on the subject: http://viewsourcecode.org/why/hacking/theFullyUpturnedBin.html
Answer: It can be particularly bad to create symbols from user input without validating the input against some kind of a white-list (for example, for query string parameters in RoR). If user input is converted to symbols without validation, a malicious user can cause your program to consume large amounts of memory that will never be garbage collected.
Bad (a symbol is created regardless of user input):
name = params[:name].to_sym

Good (a symbol is only created if the user input is allowed):
whitelist = ['allowed_value', 'another_allowed_value']
raise ArgumentError unless whitelist.include?(params[:name])
name = params[:name].to_sym

Answer: Starting Ruby 2.2 and above Symbols are automatically garbage collected and so this should not be an issue.
Answer: If you are using Ruby 2.2.0 or later, it should usually be OK to dynamically create a lot of symbols, because they will be garbage collected according to the Ruby 2.2.0-preview1 announcement, which has a link to more details about the new symbol GC.  However, if you pass your dynamic symbols to some kind of code that converts it to an ID (an internal Ruby implementation concept used in the C source code), then in that case it will get pinned and never get garbage collected.  I'm not sure how commonly that happens.
You can think of symbols as a name of something, and strings (roughly) as a sequence of characters.  In many cases you could use either a symbol or a string, or you could use a mixture of the two.  Symbols are immutable, which means they can't be changed after being created.  The way symbols are implemented, it is very efficient to compare two symbols to see if they are equal, so using them as keys to hashes should be a little faster than using strings.  Symbols don't have a lot the methods that strings do, such as start_with? so you would have to use to_s to convert the symbol into a string before calling those methods.
You can read more about symbols here in the documentation:
http://www.ruby-doc.org/core-2.1.3/Symbol.html


Could a single row of legs be useful?

Question: Could it be useful for a species to evolve a single row of many legs on the underside of the body? The specific organism is amphibious, and has no paired structures on the outside. It does have unpaired fins along its midline, which would be the origin of these legs
Comment: How many legs? Two?
Comment: My suspicion is that they could be made useful, even if the creature might never be a sprinter. The best way to answer it definitively would be (unfortunately) a simulation sophisticated enough to test various configurations and see if any rise above some arbitrary threshold. Get me a $200k grant and I'll get to work on that.
Comment: Would it depend on the direction of movement - two legs one front and one back for a creature walking sideways would effectively be the same in most ways as a "normal" bipedal creature in terms of mechanics and stability, especially if the species already has ~360 degree vision.
Comment: If your creature live on Arde, or any other planet in the Planiverse, then a single row of legs is the only possible way to do it!
Answer: probably...
The biggest issue is stability. Conceptually, it looks like this viewed head-on:

If it continuously tips over on its side, it's not going to survive long.
Since this creature is described as having "many legs", I'm going to assume it is proportionately long suggesting an eel with legs or a millipede with only half its legs. That form suggests a possible mitigation for the stability issue. If this creature never walks straight forward but always follows a serpentine path, the head-on via changes to something like this:

This, unfortunately, introduces an efficiency issue. continuously walking in serpentine path wastes a lot of energy when compared to going straight. So, maybe we just grow a proper foot to widen the base a bit. Now the head-on view looks like this:

To make this work, it'll need to evolve an ankle to handle uneven terrain. That's not impossible so it could work. But there's an arguably easier and more efficient fix. What if it pointed its center-mounted legs to alternating sides? Maybe all of the odd-numbered legs lean right, and all the even-numbered legs lean left. That gives us a head-on view like this:

Ok, problem solved. Your amphibian can now walk on land which is a definite advantage and worth doing. It even had two different approaches so they'll probably both exist. Two species for the price of one!
But...
Nothing's that easy. Over time, our angle-leg version is going to find it more efficient to move the legs out from the center. Like this:

And now, unfortunately, we've evolved two rows of legs. Oops.
conclusion
This is definitely doable but it's going to face pressure from more efficient designs (bilaterians dominate animal life forms for a reason). If this design is important to your project, I'd recommend making your setting right after a mass extinction event when evolution tries all the crazy stuff.
Answer: YES
...
and no.
Such a broad, open ended question deserves at least two hundred different  answers! I'll start with the most obvious.
First, it's obvious that such an adaptation is useful. Anyone who has access to the ancient archives of the Mar Somur, the last great empire of Mars, and who has studied the remains of Martian fauna knows of the baalgar, a kind of amphibian megafauna of the equatorial regions.
Ever since the 19th century, exoarchaeologists have been aware of the complex system of canals that criss-cross the Arean landscape, monumental works of civic engineering that carried water from one place to another. It wasn't until the first aetherionauts left Earth and set foot on Mars that the true nature of the canals and creatures that called them home became known.
As the Mar Somurian archives were discovered and translated, a picture of life on Mars in the remotest of ancient times became clear. According to the Annals of Hannunna, a kind of beast had long inhabited the abandoned canals and waterways of the long dead empires of the wastelands. Long and serpentine it was, and it was described as "having but a single row of paddle-like appendages along its ventral surface.
As the beast grew into the baalgar known to the Hannunna of the last days of Mar Somur, its body had "outgrown the grand canals made by the labours of our ancestors; and its paddles were now become heavy clubbed feet." Combined with a "thick carapace of scales along its belly", the baalgar was able to rest its body along the canal walls as it used its single row of appendages to push through the murky waters and mud of the drying water courses in its endless search for sustenance.
Of course, Terran aetherionauts could only find the skeletal remains of the beasts, and were at first perplexed. Bony plates and scales they found along the margins of the canals in the thousands, along with what appeared to be a single row of legs laid neatly to one side or the other of the spinal bones.
Theorising at first that these might be some kind rib or spinous process, it was not until the textual evidence was brought to light that the natural philosophers who have braved the sere deserts that now lay the red planet waste were able to understand the true nature of the baalgar.

Could a single row of legs be useful?


Are personal names spelled in hiragana or katakana if the kanji isn't known?

Question: I understand that a foreigners name is spelled in katakana, but wanted to know the appropriate way of spelling a Japanese persons name. Would hiragana be preferred? Would a choice be made between a foreign name (katakana) and a native Japanese name?
Answer: Whichever is fine, but katakana tends to be preferred in formal settings. For example, when you take a message over the phone from someone who only called himself Saiki, then you can say サイキ様からお電話がありました. Saiki can be 佐伯, 斉木, 西城 and so on in kanji. Writing さいき様 is not wrong, but it may look childish.
Traditionally, katakana has been used as the default script when kanji is not available for some reason. This is why old telegraphs and old computers only supported katakana.
Comment: Another common example (though technically in reverse direction of the question): some restaurants have queue sheets, where you'd write down your name and the size of your party instead of having to physically stand in the queue; the waitstaff calls your name when they are ready to seat you. One writes down one's name in katakana, not kanji, in order not to embarrass the waitstaff.
Answer: Yes, hiragana is the preferred way of spelling a name without knowing the actual characters.
Comment: I don't think it is that straightforward. The kanji names are often intentionally replaced by hiragana e.g. on the name tags of shop employees to make it easy to everyone to read. But, if we talk about a more "official / serious" use [like e.g. authorities referring to a person with a name with unknown spelling and one wants to avoid misunderstandings + make it clear that the correct spelling is not known, katakana would be preferred, as using hiragana could lead to a confusion where one might think (that even for the surname) the hiragana would actually be the correct spelling.
Comment: Hmm maybe it is! I know that I've always been taught that hiragana is the go-to in these situations and while I was studying in Japan this same question was answered this way. Of course I do see your point there.


Can I partial match a string in visual workflow?

Question: My use case is as follows
in my flow a user enters a subject into a text input field. I then place the input into a variable. I then perform a record lookup on a custom object to find any records that match that variable. I then have a dynamic choice that displays the records.
When finding records the criteria I am using is
Custom_field - Contains - Variable
this works fine when the custom field is an exact match for the text string in the variable. Example - If I enter Account team in the input field, it will find a record with a string like "I have an account team" in it. If I search "Team account" it returns null. It only matches an exact string.
What I need is to match based on any word in the string. A like function or something similar.
Is there any way to loop through a string and search each word or a way to perform a partial match?
To Confirm, The Contains function only matches an exact string. So if the variable contains "123" and the custom field on the record contains "321" it does not match.
Answer: You can pick "contains" as the operator. From the user input no need to add wild cards.


Programming ActiveSync on Windows Mobile

Question: I am developing a desktop app which manages contact information and I want to be able to have it sync with the contacts list on Windows Mobile devices.  Which namespaces/APIs do I need to understand to do this?  I would prefer something in .NET compact framework, but I can do Win32 as well.  I am looking for an approach that is completely stand alone, i.e. not dependent on a separate app such as Outlook.
Thanks
Answer: If you can work with the most recent compact framework then you can use the WindowsMobile Class Library.
If you have to work with an older version of the framework or want to support older hardware you can access the native ActiveSync API with Interop.  All of the C++ APIs can be accessed through either Interop/PInvoke or COM Interop.  An example is here.
Answer: ActiveSync does not have a managed API.  There is a sample called "stockpor" in the ActiveSync SDK folder (by default it's at C:\Program Files\Windows CE Tools\wce500\Windows Mobile 5.0 Pocket PC SDK\Activesync\Activesync stock portfolio sample) that gives you an example of how to do custom item synchronization.
EDIT:  A second option would be to use POOM for the device side, and create a custom RAPI DLL that you could interact with (it's not advised to try to directly open the contacts database, as the record fomat is not guaranteed to stay the same across WinMo versions).  You would have to do your own conflict resolution, etc. but it might be easier to get at the on-device contact info that way.
Answer: Also consider looking at Microsoft SyncFramework. Sync is a far harder problem than people realise and building a solution that caters to all the edge cases can be very difficult. IIRC they even have examples on syncing from Outlook to a Pocket PC.
If you do decide to go the RAPI route OpenNETCF have a nice RAPI C# library see here.


Tutorial first time you enter into an app?

Question: I'm programming an app using android studio. I want to know in which way I can do a tutorial that users will see only the first time that use the app. Tutorial like image or screenshoots
Can someone help me? Thanks
Answer: I encountered this thread while looking for a solution for running a tutorial only at the first time (as rbaleksandar suggested), so in case it will be helpful for someone someday, here's a template of a solution that works for me (using the SharedPreferences API):
@Override
    protected void onResume() {
        super.onResume();
        String tutorialKey = "SOME_KEY";
        Boolean firstTime = getPreferences(MODE_PRIVATE).getBoolean(tutorialKey, true);
        if (firstTime) {
            runTutorial(); // here you do what you want to do - an activity tutorial in my case
            getPreferences(MODE_PRIVATE).edit().putBoolean(tutorialKey, false).apply();
        }
    }

EDIT - BONUS - If you're into app tutorial - I'm messing now with the ShowcaseView library (which is amazing - try it out). Apparently they have some shortcut for that issue using a method called singleShot(long) - its input is a key for the SharedPreferences, and it does the exact same thing - runs only in the first activation. Example of usage (taken from here):
@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_single_shot);

        Target viewTarget = new ViewTarget(R.id.button, this);
        new ShowcaseView.Builder(this)
                .setTarget(viewTarget)
                .setContentTitle(R.string.title_single_shot)
                .setContentText(R.string.R_string_desc_single_shot)
                .singleShot(42)
                .build();
    }

Comment: Those are brilliant solutions! Thanks so much!
Answer: You could always code your own solution, but, let us not reinvent the wheel.
Check this Android Library:
Tour Guide Repository
It allows you to add pointers in your screen, so the user knows where is he supposed to touch next.
It's pretty easy to use, you only need to point to the element you want the user to touch.
From the doc:

Let's say you have a button like this where you want user to click on:

Button button = (Button)findViewById(R.id.button);

You can add the tutorial pointer on top of it by:

TourGuide mTourGuideHandler = TourGuide.init(this).with(TourGuide.Technique.Click)
        .setPointer(new Pointer())
        .setToolTip(new ToolTip().setTitle("Welcome!").setDescription("Click on Get Started to begin..."))
        .setOverlay(new Overlay())
        .playOn(button);

Hope this helps!
Comment: I am having trouble to use this TourGuide on a BottomNavigationView. I guess .playOn does not work on menu items. And compiler gave an error about (TourGuide.Technique.Click) statement. I needed to change it with .CLICK
Comment: `setOverlay()` returns void, so `playOn` can't be called after it, however, calling `playOn()` first then `setOverlay()` should work
Answer: Some links to libraries for creating introduction and/or tutorial screens.
Horizontal cards like Google Now:
https://github.com/PaoloRotolo/AppIntro
Tutorial screen:
https://github.com/amlcurran/ShowcaseView
Comment: Thanks...I like so much the style!
Answer: As far as I understand the question is not How do I create a tutorial? (as the people who have already posted an answer have concluded) but instead How to show a tutorial upon first launch only?. So here are my two cents on this topic:
I'm not familiar with how your Android app stores its configuration data but I will assume that it's either in a database (SQLite) or a text file (plaintext, YAML, XML - whatever). Add a configuration entry to wherever the app's settings are being stored - something like tutorial_on : false, tutorial_on : 1 etc. depending on the format the configuration is represented in.
The way configurations work is that whenever an app (or software in general) is launched it has to be loaded in the app itself. So add the following to your app (where and how is up to you and your app design):

Check tutorial_on entry
If tutorial_on is set to true/1 whatever
2.1 Display tutorial
2.2 Change tutorial_on to false/0 whatever
2.3 Store the result in your configuration
Continue using the app

By doing so the first time your app launches the flag responsible for displaying the tutorial will be toggled and afterwards every time you start the app the toggle flag will be read leading to omitting the tutorial.
Personally I would suggest that you an option similar to Don't show tutorial anymore along with a description how to re-enable it (by triggering some action in that app's menu etc.). This has two major benefits:

Improved user experience - users like to have control (especially over trivial matters such as showing or hiding a tutorial). Whenever you take the control away from them, they get pissed off.
Enable your user to re-learn forgotten things - a general rule of thumb is to create apps that should not burden the user with a lot of stuff to remember. That is why things should be self-explanatory. However sometimes you may want to do that nonetheless. By adding the possibility that the user re-launches (by simply resetting the tutorial_on flag and repeating the steps from above) the tutorial allows just that - refreshing a user's memory.


Representing momentum exchange in Feynman diagrams

Question: I'm a bit confused about how momentum exchange is represented in Feynman diagrams. I'm going through Tongs qft notes on interactions right now and he demonstrates how to draw Feynman diagrams with a few examples using the scalar Yukawa interaction. For nucleon-nucleon scattering the exchange particle is said to be a virtual meson. For the decay of a nucleon-antinucleon pair into two mesons the exchange particle is a virtual nucleon. For meson-meson scattering Tong states that the simplest way to represent the exchange of momentum is through a loop. I don't understand how he decides what particle(s) to use for momentum exchange. Can someone please point me in the right direction?
Answer: Each interaction is given by a term in the Lagrangian (density), which in the case of Yukawa interactions is
$$\mathscr{L}_Y = g \bar{\psi}\psi \phi, $$ where $\psi$ and $\phi$ are the field operators of nucleons and mesons, each containing the corresponding creation/annihilation operators.
This term is what determines what are the possible interactions. It tells you that every vertex must join exactly two nucleons/antinucleons and one meson, so for two mesons to scatter you must use at least four such terms: at each vertex there can only be one meson $\phi$, so you need two vertices for the two incoming mesons to annihilate into nucleon/antinucleon pairs, and now you need another couple of vertices to turn the (virtual) nucleons/antinucleons back into a pair of outcoming mesons.
Comment: That makes a lot of sense, thank you. Just to be sure that I'm clear on this, does that mean for $\phi^4$ interactions we will have four mesons at each vertex?
Comment: Yes that's right.


IP Man Half Sitting Stance

Question: What is this stance called? How do you train it step-by-step?
Comment: Strength-show-off-stance? Why do you want to train that stance, which quite obviously has no fighting applicability?
Comment: @Philip Klöcking in my country quite a lot come to us for TV shooting and interview .. perhaps sometime need some stance that audience would like to see :D
Comment: @Philip Klocking Actually just about every style has stances that have no fighting applicability.  Bowing in Judo for example is not a combat stance but there is still a perfectly good reason for doing it.  See also press-ups.
Comment: There's really only one practical purpose to this stance. And that's to increase muscle strength. It's a pistol squat. With a complete calisthenic program, which includes these squats, you can adapt to disadvantageous positions much more quickly. Some may actually put themselves in such a position to execute a surprise move, a la capoeira. These are risky moves, though, and if it goes badly, the result can be a snapped knee. Not for everyone! For the young and athletic, perhaps.
Comment: perhaps some motivation to train more too with some targets
Comment: @HuwEvans While I agree that every martial art has *training forms* that have no applicability in fighting, I have to point out that bowing is not a judo stance but a mere social ritual showing mutual respect. It is not even Judo proper, it is cultural context.
Comment: @SteveWeigand Please write an answer.
Answer: It's (a very exaggerated) cat stance (Mao Bu - Xuán Jī Bù)(玄機步)
Instructions from Skimble:

Place entire body weight on a single leg like a squat and extend the other leg in front to lightly touch the ground. Since the frontal leg has no weight placed on it, it can be used to launch fast kicks. It is sometimes used in conjunction with other stances for evasive actions. Switch sides halfway through if possible.
Comment: As I think the description is a bit off/incomplete: Any kick you can launch from there can only be an interruption/distraction since there cannot be any power behind that. This stance is usually not *held* in fighting - and if so, certainly not as deep as in the OP and some of the pictures on this site - but used as a short transitional state when you e.g. move back to evade a kick but want to go back forwards fast. That being said, one-legged deep squats with the other leg forward are a standard strength exercise for the gluteus and quads in many martial arts.
Comment: @PhilipKlöcking Agreed, that's why I wrote it's exaggerated.
Answer: While it's not Wing Chun, we call that stance negativa (negative) in Capoeira, specifically the Régional version. We typically have one hand on the ground for support (on the side of the extended leg), the other guarding the head, and a slight tilt forward of the torso. It's used as a dodge, typically combining both moving backwards and down to avoid a kick, and it's often followed by a rôle, a roll, with the raised arm parking across the body to support the capillary straw in an inverted position, and is sometimes also used to start the momentum for a spinning kick.
Ask for how one trains for the position, a lot of it is very similar to learning a pistol squat, or just a regular body weight squat. You need to have some degree of flexibility of the ankles and knee, as well as a decent amount of leg strength, especially if you plan to lower into the position, or rise from it, using that bent leg as the support with minimal use of your hands. We usually start by having people go down into a squat, and then extending one leg, to get used to having that one leg bent underneath you, and supporting your weight. As the legs strength and flexibility increases, we have people transition from a stance with one leg forward to shifting their weight backwards into the negativa. For descending straight into it, we typically use the same methods as with pistol squats, starting out by using the arms more to absorb going down, and working towards going down more slowly.
As a side note, where the supporting leg is placed varies based on flexibility. I personally use something closer to what's shown above because my knee tends to get strained as my calf and thigh meet, but the classic position involves being up on the ball of the foot with the supporting leg underneath your hips to make it easier to shift forward if you desire.
Comment: This is not negativa. Other than the supported hand, the negativa is dynamic, while the stance is static.
Comment: @AlaychemgoestoCodidact {waggles hand} no stance should be truly static, except perhaps when training, to develop muscular fitness and endurance.
Comment: Yeah, but you might wait on cat stance for opponent's move, but you never wait on negativa
Answer: I believe the closest of this is the pistol squat.
Here is the video and how to train step by step
Pistol Squat Step by Step

Benefits are training to be more focus and balance which align with Wing Chung teaching.

IP Man Half Sitting Stance


Computed field value in twig template

Question: I use a computed field, to calculate and store a floating value for a node. Now I want to work with this value in a twig template. When I access the field value via {{ content.computed_field.0 }}it outputs the correct value, say 0.22. When I try to calculate with this value, i.e. {% set newvalue = content.computed_field.0 * 100 %} the page breaks (just pre-calculation twig content is outputted).
My first guess was that, for some reason, the field value is stored or read as a string (or another type?!). My DB says its a float and I don't know how to check a variable type in twig.
I tried to to use twigs number_format()-function : {{ content.computed_field.0|number_format(2) }}. This transforms the computed field to 1. I have no clue why this happens.
What am I doing wrong? Any tips or a workaround?
I use Drupal 8, Twig 1.25, and Computed Field 8.x-2.0-alpha3
Thank you in advance
Comment: Why can't you make a math in field preprocess function?
Answer: You could try this, if your using a node template:
{{ node.computed_field.value * 100 }}

Computed field value in twig template


Can I quit claim deed my property to anyone I want?

Question: I would like to transfer my property to a random person I do not know by quit claim deed. Can I do that?
Answer: Yes you can. You will probably need the person's full name and address. You will probably need to pay a notary fee, and possibly a registration fee at whatever government office handles land titles in your jurisdiction. The recipient might chose to decline.
Answer: You may have a small problem complying with local law (e.g. RCW 64.04.050), if the deed is required to have a "consideration" clause. If the grantee gives you something in return, you're okay. The typical "love and affection" clause would be untrue in such a case. This is not insurmountable.


How to create a soap client without WSDL

Question: i need to visit a secure web service,
every request in the header need to carry a token.
i know the endpoint to the web service,
i also know how to create the token.
but i cannot see the WSDL for the webservice.
is there a way in C#, to create a soap client, without the WSDL file.
Comment: Possible duplicate: http://stackoverflow.com/questions/278037/soap-client-in-c-without-access-to-a-wsdl-file
Answer: I have verified that this code, which uses the HttpWebRequest class, works:
<code>// Takes an input of the SOAP service URL (url) and the XML to be sent to the
// service (xml).
public void PostXml(string url, string xml)
{
    byte[] bytes = Encoding.UTF8.GetBytes(xml);
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    request.Method = "POST";
    request.ContentLength = bytes.Length;
    request.ContentType = "text/xml";

    using (Stream requestStream = request.GetRequestStream())
    {
       requestStream.Write(bytes, 0, bytes.Length);
    }

    using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
    {
        if (response.StatusCode != HttpStatusCode.OK)
        {
            string message = String.Format("POST failed with HTTP {0}",
                                           response.StatusCode);
            throw new ApplicationException(message);
        }
    }
}
</code>
You will need to create the proper SOAP envelope and pass that in as the "xml" variable.  It takes some reading.  I found this SOAP Tutorial to be helpful.
Answer: A SOAP client is simply an HTTP client with more stuff in it. See the HttpWebRequest class. You'll then have to create your own SOAP message, perhaps using XML Serialization.
Answer: You could create your own service, expose it to have a WSDL and then generate the client from that... kind of the long way.
Answer: Can you ask the developers of the web service to send you the WSDL and XSD file(s) by email? If so, you can dump the files in a folder and then add a Service Reference using the WSDL on your hard disk.


Will Randall-Sundrum extra dimension scenario become defunct if not supported by LHC?

Question: The Randall-Sundrum extra dimension scenario had been one of the most extensively studied class of theories. This offered a solution to the hierarchy problem. However, if this picture is not supported by the LHC, will it become completely defunct? What about theories like little higgs, composite higgs, technicolor, higgsless models (perhaps already practically abandoned?)?
Answer: If the LHC never discovers physics beyond the Standard Model (in its 1-decade-long career, roughly speaking), than sometime during its research – depending on the physicist (for some of them, the moment has already arrived, but those may be highly premature decisions) – there comes a moment when most physicists decide that the hierarchy problem is not solved "quite naturally" in the old-fashioned sense and Nature simply tolerates at least some fine-tuning.
This has the same effect on all the classes of models you suggested – and others. That's why it's irrational to single out one class of models that attempted to make the lightness of the Higgs natural. But many of these models, including Randall-Sundrum, still have other motivations to be studied even if they don't quite account for the hierarchy problem.
Even when it comes to the hierarchy problem, the LHC isn't able to "totally" show that Nature is unnatural. There are surely people, and I have always counted as one, who find 1-in-1,000 to be a tolerable amount of fine-tuning. So many physicists will still believe that new physics is "relatively close", whatever it exactly means, and their research will reflect this belief.
Comment: +1, if fine-tuning is going to be accepted, then a robust relationship between a light Higgs and the anthropic principle must be developed. as far as my limited understanding and every-day experience says, the mass of the Higgs by itself does not imply any correlation with stable complex chemistry or long-lived star systems. Maybe there are other consequences that are still amiss?


Is it possible to add a column to a partition in a partitioned table?

Question: I have a large partitioned table of 16 billion plus records. I am currently updating one of the columns to NULL using the partition number. The process is cumbersome in that it takes a lot of time to complete the operation. One of the partitions of 70 GB took 11 hours to complete the update.
So my question is, is it possible to create a column within a partition so that I can use it to do the update in a faster way?
Ideally I'd like to create the new column with NULL values, then delete the old column and rename the new one to the same name, rather than update billions of rows
i.e.
create NewColumn with null values
rename CurrentColumn to  CurrentColumn_delete
rename NewColumn to CurrentColumn
Delete CurrentColumn_delete
but only on the partition and not whole table
Comment: "*One of the partitions of 70 GB took 11 hours to complete the update.*" - This sounds like an architectural problem. 70 GB is not a lot of data and shouldn't take even an hour to update, let alone 11 hours. Kind of sounds like your real problem is understanding why that took so long, which we probably can help you figure out if you want to add details about your schema, the data, the `UPDATE` query used, it's execution plan if possible, and some examples.
Comment: This raises several questions. What version of SQL server are you using? Are you doing the update in one enormously long transaction or did you attempt to break the update procedure to batches, for example 100K rows per transactions? Breaking up the transaction to several smaller batches could yield faster processing.
Comment: @Sranda Thank you for your response. I am using SQL SERVER 2017.I am running the update in one enormously long transaction and this is per partition and the amount of data in each partition varies. In regards to your suggestion, how do I update the records in batches?
Answer: To answer a question of "how do I update the records in batches" with brief comment:
DECLARE @i INT = 1;
/*here you say how many records would you like to update at once*/
DECLARE @batchsize = 100000;
WHILE EXISTS(SELECT TOP(1) * FROM [table] WHERE col_X IS NOT NULL)
BEGIN
    print @i
    BEGIN TRAN
        UPDATE TOP(@batchsize) [table] SET col_X = NULL WHERE col_X IS NOT NULL;
    COMMIT
    SET @i = @i+1
END

This is rather to demonstrate the concept than give you the solution tailored to your needs, because:

no error handling is in the code
as J.D. said, we'll need to get deeper insight to your data and schema
the less rows will meet the condition of not being NULL, the slower the update will be (it will be more difficult to find them)

Other thing that could be relevant to you is to check the indexes on the table - in how many indexes is the updated column used? Not only the table but each index has to be updated too and it goes single-threaded - it influences your performance a lot.
Regarding the rename - it is metadata operation only (but for the whole table) and you could use the following snippet:
ALTER TABLE [table] ADD colX_new int;
EXEC sp_rename '[table].colX' , 'colX_old';
EXEC sp_rename '[table].colX_new' , 'colX';

I don't think you can add column to individual partition only.


Do you use Personas?

Question: I wonder how many UX designers user Personas to create design.
Comment: I don't agree such a question should be closed. We can not treat this forum, covering the emerging and subjective field of UX- as other stablished, objective fields such as programming.
 Creativity and design are big part of the field hence it is not always a right or wrong answer to questions.
Many answers to some still valid questions can be based on opinion and personal experience which is not always destructive. in particular since the filed still suffers from limited num of of reliable sources in some aspects.
Answer: I use personas; they're a great way of keeping the user in the room whenever design decisions are being made.
However, there's a risk, especially if ux thinking and practice is spreading beyond the confines of my own desk (a good thing). The risk is that others may not realise that a persona is simply a way of presenting user research. The persona lives and dies by the quality of that research. There is sometimes a temptation for a project team to simply 'invent' a persona, based on nothing but their own ideas about who the users are likely to be. Once constructed, a convincing (though factually empty) persona can be difficult to kill off.
Also, I've seen personas created as a design deliverable, and then forgotten about. The act of creating the persona is not where the value lies - remember that the persona itself is just a form of report on user research. It's value is in its constant use through the project lifecycle, the repeated question, 'would Simon like this?', 'would Sarah understand that?' It's a means of injecting the results of user research into the heart of the design and development process.
Comment: +1 the "keeping the user in the room" metaphor (probably a phrase you use all the time) is a great way to grasp that point.
Answer: Yes.
A good, well-researched understanding of the people you're designing for is important to guide design decisions and then later on provide as the rationale for your design when (inevitably) questioned. The effort you go to to develop qualitative and quantitative datasets that you develop your personas from can vary depending on how important they are to the design process, how much time you have, how much room there is to customise the solution based on personas (there may be an very strict design already imposed) and other requirements and constraints.
Comment: +1 this answer gave me increased depth of my understanding of personas
Answer: I find personas work wonders if you have all the information about the target audience and the expected user base. I was asked to do some persona testing the other day and while I succeeding in delivering something quite basic based on perceived journeys, I ran the risk of making my personas stereotypes which leastens the value of the excercise. But hand in hand with knowledge about the users this is a much cheaper way of getting real value out of testing without making use of labs or remote testing.
Answer: I'm trying to drive our organisation towards using them more than we have done in the past. I think it's vital to design for an audience and the more detail who have about that audience, or the more specific you can make it, the more you'll be able to tailor the experience.
There are obviously times where it is less appropriate than others, but most applications we develop have a business purpose and thus multiple levels of business users. Their needs/expectations/role needs to be right at the top of our considerations when it comes to how the application will operate.

Do you use Personas?


burying the neutral to used less cable for welding a long way from the power source

Question: Of course we are not talking about code or best practice, but hypothetically if someone wanted to do some welding a few hundred meter from the closed power point could he/she run one hot conductor to the site and just bury the neutral in the ground and get to welding?
Comment: https://en.wikipedia.org/wiki/Single-wire_earth_return
Comment: A similar question came up some time ago. It turns out that there are some places in some countries where the earth has been used as a conductor. But I believe this was done with much higher voltages and lower currents and longer distances. I doubt you will get good enough conductivity for a low voltage welder. (Low voltage meaning less than 500 V).
Answer: Aside from (obvious?) danger, the typical ground resistance is too high for that to work.
Answer: Chris's question is not 100% clear. Leaving aside safety and the rest, and focusing on feasibility, it may be interpreted as if you have a conductor in the soil or the soil alone.

conductor in the soil, as a grounding system nearby: provided cross sections are sufficient (e.g. refer to BS7671 or IEC 60364-4-41 for the cross sections that should be used if you ground your "equipment", or make a full calculation with BS7430 or IEC 60364-5-54). Of course, if there are other users of the same grounding system, the might be affected by the sudden current spikes flowing in it.
using soil alone, as @mkeith said, it depends on the soil resistivity. When you perform soil resistivity measurements, your instrument tells you first the resistance between the voltmetric electrodes and then calculate the soil resistivity: the former values are not so large, in the order of some ohm for most soils.

Example: a soil resistivity of 33  ohmm, gives you 0.5 ohm for a measurement at 12 m separation. The wider the separation the larger also the depth of the ideal half sphere between the two electrodes and thus the used volume of soil.
If you are some hundreds m apart you have a some hundreds m long some hundreds m deep half sphere; in common soil with less than 100 ohmm resistivity it gives you let's say 1 ohm.
Two ingredients: Now, what you need is i) good coupling with the soil, and ii) the possibility of putting so much current in the soil from your Low Voltage distribution (protection relay!). i) good coupling = you must bury a copper conductor of several meters, or better a metallic plate or large tape (see IEEE Std. 80 or BS7430 for its resistance). ii) your welding machine must be insulated by a transformer otherwise zero sequence relay will trip, or remove the relay.

Now: isn't it easier/safer to bring a long three-conductor cable sized for the voltage drop, such as a 3x4 mm2 and put your welding machine there near the point where you want to work? A bit more expensive in terms of Cu$ (copper money), but easier and linear to implement.
Answer: No
Again No
Not safe, not advised to even dream about it.
Comment: I was scandalized, but it is happing right now.... i just want to understand the physics of how it is working .
Comment: @chrisalyui the physics is really not complicated. Current is flowing through the ground instead of a wire.
Answer: Hypothetically, ignoring all safety and such, it could work if and only if the resistance of the ground leg is small enough to conduct enough current for the welder to do its job. I know that very dry soil, and hard frozen soil and bedrock do not conduct electricity very well. So the best chance for success would probably be in a place where there is lots of damp soil.
I have never measured soil conductivity quantitatively and I am not sufficiently motivated to research the topic. But I know from experience and lore that electric fences become ineffective in very dry climates and hard frozen climates due to the lack of conductivity in the soil.
I also know from a previous question and answer that in some cases, power is actually distributed from utility companies via a single wire, relying on earth to return the current to the source. Here is the wikipedia:
https://en.wikipedia.org/wiki/Single-wire_earth_return
Note that in the case of utility installed systems there is an isolation transformer involved and customer premise wiring does NOT use soil or earth as a current carrying conductor.


Visual Studio Express 2012 and Git

Question: Can the IDE level version control support in Visual Studio Express 2012 be used with Git, or would that require plug-in support available only with the full version?
Answer: Actually, the selected answer is wrong. Visual Studio Express 2012 supports Microsoft's plugin for Git, as it's actually an extension of Team Foundation. You can find it here: http://visualstudiogallery.msdn.microsoft.com/abafc7d6-dcaa-40f4-8a5e-d6724bdb980c
However as of today there are a couple of bugs in the installer preventing from installing it - this is a bug, and will be addressed in a future release (check the comments of the project to see Microsoft's response).
Answer: Express Editions of Visual Studio 2012: no other plugin supported, except the one (Git Plugin) built by Microsoft.
Comment: Plugin is downloadable here: http://visualstudiogallery.msdn.microsoft.com/abafc7d6-dcaa-40f4-8a5e-d6724bdb980c and supports Express versions.
Comment: @linquize: You're free to update your answer in order to provide the correct information for the new situation.
Comment: Who downvote? In Dec 2012, no such announcement was made! MS announced this in late Jan 2013!
Answer: Have you tried TortoiseGit? I know the preferred choice would be to use a plugin but with the Express is not possible. It happened to me with Ankhsvn when I started with the Express. I don't know if it is a good tool, you can give it a go: https://tortoisegit.org/

Visual Studio Express 2012 and Git


Can I use BioEdit to quantify the sequence similarity?

Question: I am using BioEdit. It can perform an align of multiple sequences. Can this sequence similarity be outputted as a value, e.g. 70%?
Answer: No Bioedit is an alignment editor only. It is not in anyway an analysis program.
Dump the format in fasta or mega (its the option is available) and import it into Mega X here. You can quantify the diversity as a pairwise matrix, population analysis (if you have a clear a priori that you can subdivide your sequences into different groups) or phylogeny ... which provides diversity as mutations per alignment position. Its pointy and clicky and easy to use.


Caret - Repeated K-fold cross-validation vs Nested K-fold cross validation, repeated n-times

Question: The caret package is a brilliant R library for building multiple machine learning models, and has several functions for model building and evaluation. For parameter tuning and model training, the caret package offers 'repeatedcv' as one of the methods.
As a good practice, parameter tuning might be performed using nested K-fold cross validation which works as follows:

Partition the training set into 'K' subsets
In each iteration, take 'K minus 1' subsets for model training, and keep 1 subset (holdout set) for model testing.
Further partition the 'K minus 1' training set into 'K' subsets, and iteratively use the new 'K minus 1' subset and the 'validation set' for parameter tuning (grid search). The best parameter identified in this step is used to test on the holdout set in step 2.

On the other hand, I assume, the repeated K-fold cross-validation might repeat the step 1 and 2 repetitively as many times we choose to find model variance.
However, going through the algorithm in the caret manual it looks like the 'repeatedcv' method might perform nested K-fold cross validation as well, in addition to repeating cross validation.

My questions are:

Is my understating about the caret 'repeatedcv' method correct?
If not, could you please give an example of using nested K-fold cross validation, with 'repeatedcv' method using the caret package?

Edit:
Different cross validation strategies are explained and compared in this methodology article.
Krstajic D, Buturovic LJ, Leahy DE and Thomas S: Cross-validation pitfalls when selecting and assessing regression and classification models. Journal of Cheminformatics 2014 6(1):10. doi:10.1186/1758-2946-6-10
I am interested in "Algorithm 2: repeated stratified nested cross-validation" and "Algorithm 3: repeated grid-search cross-validation for variable selection and parameter tuning" using caret package.
Answer: There's nothing wrong with the (nested) algorithm presented, and in fact, it would likely perform well with decent robustness for the bias-variance problem on different data sets.  You never said, however, that the reader should assume the features you were using are the most "optimal", so if that's unknown, there are some feature selection issues that must first be addressed.
FEATURE/PARAMETER SELECTION
A lesser biased approached is to never let the classifier/model come close to anything remotely related to feature/parameter selection, since you don't want the fox (classifier, model) to be the guard of the chickens (features, parameters).  Your feature (parameter) selection method is a $wrapper$ - where feature selection is bundled inside iterative learning performed by the classifier/model.  On the contrary, I always use a feature $filter$ that employs a different method which is far-removed from the classifier/model, as an attempt to minimize feature (parameter) selection bias.  Look up wrapping vs filtering and selection bias during feature selection (G.J. McLachlan).
There is always a major feature selection problem, for which the solution is to invoke a method of object partitioning (folds), in which the objects are partitioned in to different sets.  For example, simulate a data matrix with 100 rows and 100 columns, and then simulate a binary variate (0,1) in another column -- call this the grouping variable.  Next, run t-tests on each column using the binary (0,1) variable as the grouping variable.  Several of the 100 t-tests will be significant by chance alone; however, as soon as you split the data matrix into two folds $\mathcal{D}_1$ and $\mathcal{D}_2$, each of which has $n=50$, the number of significant tests drops down.  Until you can solve this problem with your data by determining the optimal number of folds to use during parameter selection, your results may be suspect.  So you'll need to establish some sort of bootstrap-bias method for evaluating predictive accuracy on the hold-out objects as a function of varying sample sizes used in each training fold, e.g., $\pi=0.1n, 0.2n, 0,3n, 0.4n, 0.5n$ (that is, increasing sample sizes used during learning) combined with a varying number of CV folds used, e.g., 2, 5, 10, etc.
OPTIMIZATION/MINIMIZATION
You seem to really be solving an optimization or minimization problem for function approximation e.g., $y=f(x_1, x_2, \ldots, x_j)$, where e.g. regression or a predictive model with parameters is used and $y$ is continuously-scaled.  Given this, and given the need to minimize bias in your predictions (selection bias, bias-variance, information leakage from testing objects into training objects, etc.) you might look into use of employing CV during use of swarm intelligence methods, such as particle swarm optimization(PSO), ant colony optimization, etc.  PSO (see Kennedy & Eberhart, 1995) adds parameters for social and cultural information exchange among particles as they fly through the parameter space during learning.  Once you become familiar with swarm intelligence methods, you'll see that you can overcome a lot of biases in parameter determination.  Lastly, I don't know if there is a random forest (RF, see Breiman, Journ. of Machine Learning) approach for function approximation, but if there is, use of RF for function approximation would alleviate 95% of the issues you are facing.


Two different length antennas can cause problems?

Question: I am using two 443 MHz transceivers (FY-605 transceiver) with both having different antenna lengths. One antenna is around 12cm long and the other antenna is around 17cm long. Will this cause problems? And does it affect the range or doesn't it work at all? Also the ±12cm antenna is connected to the transceiver with a coax cable. As far as I know this doesn't cause harm. Can anyone confirm this for me?
Comment: There are a whole bunch of things that could cause this lower range. One that springs out is the coax - type and length could be critical at 434MHz
Comment: Have you tested this? You are going to get better answers doing tests.
Comment: Well I haven't tested it, it is a project someone else worked on. He said that it all worked but the range was very disappointing. after like 200m the signal was bad. The transceivers should easily handle 500m, and I read some reviews that they got a lot further then just 500m. Also i only have those two antenna's so i can test the difference between 2 antenna's of the same vs the current setup
Comment: Ok thanks, I will try to move the parts in the unit so I can remove the coax cable and move the transceiver closer to the side of the unit so the antenna can be connected with no cables needed
Answer: As Andvaka said, there are many things that could be affecting range.  For this to be properly answered, more information should be given.  Without this information, I am assuming you are using two quarter-wave monopole antennas.  Any change in length from the ideal quarter-wavelength length will, most likely, degrade the performance of the antenna.  In order to properly design these antennas, a network analyzer would be needed to tune the antenna for the given environment (most things within the near-field range of the antenna will affect its resonance frequency).  Without this equipment, I would design their lengths to be a quarter-wavelength in length.  Also, since this type of antenna works with a single-ended signal, you need to ensure that you are actually feeding the antenna with a single-ended signal and not a differential signal.  In addition to all this, make sure that the antenna are oriented so that there is no cross-polarization mismatch.  This essentially means that both antennas should be oriented in the same fashion, i.e., both vertical.  I hope this helps...
Comment: Ok, I just looked up the manual for the transceiver.  I thought you were trying to built your own antennas.  I understand now that this is not the case.  Measure from the pivot point to the end, its not exact but you can determine from that whether it is roughly a quarter-wavelength.  The antennas proposed in the user manual are called quarter-wavelength monopole antennas; this is most likely what you have.  With that being said, some antennas have what are called loading coils built into them, if this is the case, the antenna will measure short of the quarter wavelength.
Comment: A loading coil would not necessary give an antenna more gain as compared to an isotropic antenna; it simply allows for a shorter antenna to still be efficient at radiating energy.
Comment: I will try to get some more information about the antenna's tomorrow. I didn't bought the antenna's myself, someone who was working on this project before bought them. Just one more question, the length of the antenna should be measured from the 'screw' till the end of the antenna or the point where you can orientate it horizontally or vertically?
Comment: Does a lading coil give the antenna more gain? The person who worked on this before said that one of the antenna's had more gain then the other but he didn't say which one it was. And what happens if one antenna is with a loading coil and one without?
Comment: is there a way to see if the antenna is a monopole antenna? I'm not that experienced with antenna's.
Comment: Also what I forgot to mention is that next to the 433MHz antenna is a WiFi antenna (5,1 GHz). Is it possible that the WiFi antenna interferes with the 433MHz antenna?
Comment: Here's a monopole antenna: [link](http://www.readymaderc.com/store/bmz_cache/4/424c1c29f84c6fde800cd3a3ee19bce8.image.750x506.JPG)


Accuracy of physics laws

Question: How accurate are physics laws? For example, for newtons' first law $F=ma$, if we can get a measurement of both force, mass and acceleration with a percentage of uncertainly close to $1\times 10^{-9}\%$, will the formula match the value we determined? If not, how many percentages of error could we take and still believe the law still hold?
Comment: Might there be a difference between the laws of physics and the results you or I or anyone else calculates?
Comment: @RobbieGoodwin Yes: firstly, besides the errors in calculations, they may use different approximations, or take into account different effects relevant to experimental situation; secondly, what one *calculates* and what one *measures* are rarely the same thing.
Comment: @Vadim Thanks and that wasn't quite my point.

What you said was true but it applied only to the experiments, not the laws. Whether you concentrate on calculation or measurement still, I sincerely hope the Question had nothing to do with differences of that kind.

For example, with =, if we work with accurate measurements of the initial conditions, why might we not expect accurate results? Why might  1×10−9% matter in terms of the laws?
Answer: Accuracy can mean different things. While the question asks about the statistical accuracy, what immediately comes when talking about the Newton's laws is that they are non-relativistic, i.e., they are valid up to small corrections of order $v/c$.
Physics laws are based on empirical observations, the symmetries of the universe, and approximations appropriate for a given situation.
Symmetries
For example, we have reasons to think that conservation of momentum or energy are exact laws, since they follow from the symmetry of space in respect to translations in space and time (Noether's theorem). Testing these laws in practice will necessarily result in statistical errors, but improving the precision of measurement is unlikely to uncover any discrepancies.
Approximations
Newton's laws are valid only in non-relativistic limit. Thus, they will hold only up to small corrections of order $v/c$ where $v$ is the speed of the object and $c$ is the speed of light. If our relative statistical precision (in measuring the force, acceleration, etc.) is of order $v/c$, we will observe deviations.
Empirical observations
Laws of thermodynamics are a good example of the laws that were deduced phenomenologycally, as a result of many observations. Yet, statistical physics shows that they hold up to very high precision ($\sim 1/N\sqrt{N_A}$, where $N_A$ is the Avodagro constant). If the precision could be so high or when dealing with systems where the number of particles is not small, we will observe deviations from these laws.
Remark
I recommend the answer by @AdamLatosiński, which is technically probably more correct than mine. What I tried to explain in my answer is how the laws of physics are different from, e.g., the biological laws (since the subject was recently debated on this site) - the latter are generalizations of many statistical observations, but not grounded in reasoning about fundamental properties of the universe. They are therefore statistical laws, which are bound to be non-exact. Indeed, even the so-called Central dogma of molecular biology ($DNA\rightarrow RNA \rightarrow Protein$) is broken by some viruses, performing reverse transcription ($RNA\rightarrow DNA$.)
Comment: I believe it's the difference between the precision and accuracy. The measurement may be imprecise, the law may be unaccurate.
Comment: @AdamLatosiński yes, indeed - my thinking was in a  different direction, butw hat you say is correct.
Comment: What do you mean by the term "statistical accuracy". Accuracy is stated going either way (measured value compared to law or law compared to measured value) by using only one measured value and only one "truth" value. We need not invoke statistics. Also, what other "different things" can accuracy mean that are equally valid? Isn't accuracy in this case simply "Is (law X) different from (observation Y) to this degree of confidence?
Comment: @JeffreyJWeimer *Accuracy* here is meant as a non-technical term. The accuracy that you are talking about is what I called *statistical accuracy*, as it refers to measurement. However the "truth" itself is inaccurate (as in phrase *accuracy of physics laws*). Note that *confidence intervals* is actually a very statistically involved concept from hypothesis testing (see my other recent answer here https://physics.stackexchange.com/a/626076/247642)
Comment: I will follow up separately.
Answer: There are errors that come from measuring the quantities and errors that come from the inaccuracy of the laws themselves.
If we know only approximate values of parameters in the equation, then we can calculate how precise the result it using formulas for the propagation of uncertainty. For example, for the formula $F=ma$ we have
$$ \frac{\sigma_F}{F} = \sqrt{\left(\frac{\sigma_m}{m}\right)^2+\left(\frac{\sigma_a}{a}\right)^2}$$
where $\frac{\sigma_m}{m}$ is the precision of the measurement of mass and $\frac{\sigma_a}{a}$ the precision of the measurement of accelerations. When you measure all three quantities, you can then check whether $\frac{F}{ma} = 1$ with the precision obtained by the appropraite formula, specifically you calculate
$$ \sigma^2 = \left(\frac{F}{ma}\right)^2 \left(\left(\frac{\sigma_m}{m}\right)^2 +\left(\frac{\sigma_a}{a}\right)^2 +\left(\frac{\sigma_F}{F} \right)^2 \right) $$ and, given measured values of $m$, $a$, $F$ you calculate $\left|\frac{F}{ma} - 1\right|$ and compare with $\sigma$. If it's of order of $\sigma$ or lower, it's generally considered within expectation: these kind of error may be just a result of imprecise measurement. If it's around $3\sigma$, then it may be a reason to check whether your measurement was done properly, but it can still happen from time to time. A deviation much bigger than $\sigma$ means that either your measurement is done wrong or the law is unaccurate.
Speaking of accuracy: regardless of the precision of measurement the laws themselves may be more or less accurate depending on the situation. For example, the Newton's law needs corrections that get bigger the closer the velocity is to the speed of light, and a corrected formula would be
$$ F = \frac{ma}{\left(1-\frac{v^2}{c^2}\right)^\frac32} $$
For $v=1 \text{ km/s}$ we have $$ \frac{1}{\left(1-\frac{v^2}{c^2}\right)^\frac32} \approx 1+1.67 \cdot 10^{-11}$$
while for $v=200 000 \text{ km/s}$ we have $$ \frac{1}{\left(1-\frac{v^2}{c^2}\right)^\frac32} \approx 2.42$$
So the accuracy is good for low velocities (if your measurement precision is of order $10^{-9}$ you won't see any unaccuracy) and weak for high velocities (easy to notice even with low measurement precision).
Comment: Isn't Newton's second law, in relativistic form, $\mathbf{F}=\frac{d}{dt}(\gamma m\mathbf{v})$, and not $\mathbf{F}=\gamma m\mathbf{a}$?
Comment: Perhaps rather than saying that laws may be more or less accurate "depending on the situation" you might better say "depending on the the truth in the ASSUMPTIONS". By kinetic theory, nothing is an ideal gas. Yet, we engineer the behavior in real processes by the ideal gas law more often than we care to believe. It is not the situation that makes it valid, it is the high degree of confidence in the assumptions that allows us to trust it as valid.
Comment: @JacktheRanger I've assumed that the variables are independent, but if they weren't there would be an additional term.
Comment: Newton formulated his law as force equal to rate of change of momentum (called by him "impetus" I think), not mass times acceleration; he was quite clear and explicit on this point. Relativity changes the relationship between momentum and velocity rather than the one between force and rate of change of momentum. But this does not affect the main thrust of this answer.
Comment: @JohnDumancic You're correct. I've corrected the answer, taking into the account that $$ \frac{d}{dt}(\gamma v) = \gamma^3 \frac{dv}{dt}$$
Comment: @JeffreyJWeimer Just because the assumptions are untrue it doesn't make the derived laws unaccurate. For example, a lot of the theory of gas can be derived assuming that the gas particles are tiny solid balls. This assumption is totally inaccurate, but derived equations of an ideal gas describe the behavior of real gases quite accurately in many situations. We check the accuracy of a law not by checking the reasoning that leads to it, but by comparing it with experimental results.
Comment: In further thought, kinetic theory is used to derive a formulation that explains the ideal gas law as a statement of *empirical observations*. The ideal gas law in this form is neither accurate nor inaccurate. It is valid or invalid as justified by how well the system complies to the underlying assumptions.
Comment: @AdamLatosiński Should we have the term $2\frac{\sigma_{ma}}{ma}$ inside the square root of the first equation? So its like $ \frac{\sigma_F}{F} = \sqrt{\left(\frac{\sigma_m}{m}\right)^2+\left(\frac{\sigma_a}{a}\right)^2+2\frac{\sigma_{ma}}{ma}}$
Answer: "Physical Laws" is a misleading expression.  Physical theories and models expressed as mathematics are what we have.  That does not mean the universe works that way "under the hood", it means those rules are good models to predict what will happen in given circumstances.
How Accurate a given theory is depends on three things :

How accurate you need it to be.  Why expend computational effort on a complex theory when a simpler one is "good enough" for practical purposes ?
How accurately you can make measurements to base your theory/model on.  If I cannot make measurements accurately enough to check the predictions of my theory, how accurate it is is impossible to say.
How practical is it to perform the required mathematics to make predictions.  The vast majority of practical mathematics in physics is approximate as the full blown theory is not possible to work out explicitly.

Here's a thing to remember.  The number $\pi$ turns up all over the place in mathematics (and hence in physics).  Likewise the number $e$.  But these numbers cannot be calculated exactly - no matter how you do it you need an infinite number of digits to be accurate.  So no theory, in practice, can get beyond what we can practically calculate.  Taking the $sine$ or $cosine$ of a value is likewise something you will not in general be able to do with unlimited accuracy.  Now these common functions and values have very, very precise methods to use in practice, but there are many more common functions in physics that we just have to truncate to make it practical to work with.  Something as trivial sounding as e.g. the length of an ellipse's perimeter turns out to be impossible to calculate exactly in numerical terms.  So mathematics is a practical limitation in many ways.
A very common approach used by physicists is to use a linear approximation to a non-linear model simply to facilitate using it in other models.  So we can say that $V=IR$ (relating voltage, resistance and current in a resistor), but we know it's not really that simple.  For some purposes that's as much accuracy as you need, for others you need additional terms and it becomes extremely complex.  There are multiple models of gas laws which are, in different end use cases, better or worse than each other.  It is surprisingly common to see the simplest one ($PV=nRT$) turn up places you know they are not perfect for e.g. white dwarfs.  This is because we don't always need accuracy, we need a qualitative idea of what happens and numbers that are in the ballpark are good enough for that purpose.

If not, how many percentages of error could we take and still believe the law still hold?

So after all that you will see that the law "holds" as long as it is accurate "enough" for the purpose we need.
We don't completely stop using e.g. Newton's Laws of motion just because we have relativistic theories that are better in absolute terms.  Newton works fine for so many purposes that we stick with it - There is nothing preventing a physicist going their entire career and never needing e.g. relativity (after they learn the basics for an exam).
Comment: The exact value of  is . It doesn't have an exact *decimal representation*, but most exact numbers don't. You may reason with mathematical exactitude using , as with any other exact number. For example, sin() is exactly zero. But of course, all such mathematical reasoning refers to products of the human imagination:  represents properties of such objects. Often, such objects can effectively model physical objects, but one must not confuse the model with reality.
Comment: The answer seems to carry a fallacy. The number of significant digits in a number is not a metric of its accuracy. It is a measure of its precision.
Comment: @JeffreyJWeimer The OP asked about the accuracy of theory and as theory is pure mathematics whereas actually calculating values is fundamentally limited, the precision you are prepared to apply is relevant.  Note it's not just numbers that are the issue - working with many mathematical functions is abstract and it is not always possible to treat them precisely within the limits of existing mathematics.  I can write down an equation describing a system exactly within a given theory, but that does not mean I can solve that equation.  Even numeric solutions can have high errors.
Answer: The laws of physics aren't expected to be infinitely accurate. For example, it's expected that at Plancks length, $l_P$, which is approximately equal to $1.6 × 10^{-35}~\mathrm{m}$, and which is related to Plancks constant,  is the scale where the continuum description of length, area and volume breaks down.
This is one reason why in Loop Quantum Gravity there are area and volume operators - and probably length operators, although I haven't checked - whose spectrum gives the minimal distance probeable and also why in Causal Set Theory, the discrete spacetime structure is taken as axiomatic. This also happens to be another, radical attempt at Quantum Gravity that doesn't try to quantise gravity - the bottom up approach - but builds it instead ab initio - the top-down approach.
Comment: The point was that there is nothing special about the Planck units. One Planck energy is about $10^9 J$, one wouldn't expect any interesting physics happening there...
Comment: Why should this happen at the Planck length? Why not e.g. at energy scales of one Planck energy?
Comment: @Jannik Pitt: Because I was using the Planck length as an example and besides the OP was asking about Newtons Laws and these rely on spatial measurements.
Answer: The answers given and accepted provide a well-structured set of responses.
One confusion still seems to remain. A physical law is a concisely-constructed statement about the behavior of a system or process. It is constructed to explain empirical observations in nature, and it has never been found to have been violated through the course of all past observations. We should not in this sense ask whether a law is or is not accurate. To the extent that a statement becomes accepted by calling it a law, it is accepted to be valid. We don't question its accuracy further as as statement unto itself.
Let's consider an example for a better framework on the potential confusion. The ideal gas law encompasses a statement about the observed behavior of gases under certain conditions. Real gases deviate from this law as we take them to lower temperature and higher pressure. We could propose to say that the law is inaccurate as we move to lower temperature and higher pressure (real gas behavior). I contend that we will instead be better when we say that the conditions present when the observations are made violate (go beyond) the boundaries set on the conditions required for the ideal gas law to be valid or applied to the system at hand.
It is not that the law is inaccurate as a way to represent the observation. It is that the system conditions are invalid to allow us to apply the law.
Low temperature and high pressure can have nebulous meanings as boundaries. Let's use kinetic theory or the universality framework of gas laws to express the nebulous boundaries in more meaningful ways. For any given temperature and pressure, applying the ideal gas law to predict or calculate the behavior in a system will be less valid (not less accurate) for molecules that are larger in size, have greater interaction energies (secondary bonds), or have greater degrees of inelastic collisions (viscosity). Alternatively, at the same temperature and pressure, applying the ideal gas law to predict or calculate the behavior in a system is less valid (not less accurate) for a gas at lower values of reduced temperature or reduced pressure.
Perhaps also an inverse example will help. Suppose that we make a measurement and the value does not agree with predictions from a certain law. We should not say that the law is inaccurate. We should categorically say that the measurement is not accurate against the given law because the law is invalid at the conditions present during the measurement.
Answer: I'd like to offer a simple analogy as an answer.
How accurate is a photograph, of some object, when its printed or on a monitor?
Well, its pretty accurate. That 4K monitor sure seems to show the photo of that street exactly as it looked. Except, of you look really closely, doesn't it have pixels/dots? That street scene wasn't pixelated, or was it?
Okay, ignore pixels, the colour looks right. Top notch calibrated camera, monitor and software, it should be right. Except that monitor isn't really displaying orange photons as orange, its creating the illusion of them by fooling the eye with 3 primary colours in a tiny area.
Well, suppose we let that go, and look at purely red, green and blue objects - surely those are okay? Except, that monitor only displays their brightness to 8 or 10 bit precision, because we cant see more with the eye, but photons aren't limited to those levels.  So even that is wrong, its just good enough to not see it with the naked eye.
So those photos as displayed, are not the right smoothness, or colours, or levels. So why do we think it's a good likeness at all? Because its so close, we can live with the approximations between our monitor's version of that scene, and the reality of it. We can use it the same way that Google Maps doesn't show some discarded beer can or wobbly roadside kerb, and it's still a really good guide for navigation.
But we know that if we probe deeply enough, we will probably find cases where our representation - the photo or map - isn't quite spot on. When that happens we don't declare the entire photo or map useless, we just acknowledge it always was and always will be, our best attempt to match what we understand reality to be, and with limits set by the task. For navigating to my workplace, I don't need the beer can or kerb on the map. For a crime scene I might need a highly calibrated full colour gamut photo.
And it's like that with physical laws too.
We don't know how the universe works. If we wake up tomorrow and fond it's different than we thought, that'll be reality (or delusion), and we have to deal with it. But we do find the universe so far seems to work in a way that matches very very tightly, certain formulae.
If we test and test and refine and refine those formulae, and they prove out very and over again, we might call those formulae, and the matters they represent, "Laws of Nature" or "Physical Laws".
But at best, they're just like our monitor. They are best treated as approximations of whatever reality may be, and how it seems to behave. The formulae can show us deep insights, they can predict things that we can go our and look for - and now and then they show us they are an incomplete set of formulae, because something happens in reality that isn't captured or doesn't match those formulae.
When that happens, we check reality again (ask other teams to check our findings), and then if we decide our formulae were not quite correct, we try and refine them and make better ones that keep all the strengths of our existing ones, and also match reality for the new observations as well.
And,because we expect this to happen, we constantly recheck our formulae against reality, to ever more precise and arduous tests. But we can never say "that's it", because any day, we could find a situation that our formulae don't get quite right.

Accuracy of physics laws


Given the provided Image taken at 50mm, what focal length would I need to get the 80% fo the rabbit to fill the frame?

Question:
Given the provided Image taken at 50mm, what focal length would I need to get the 80% fo the rabbit to fill the frame?
Comment: To do actual calculations we would need to know the distance to the rabbit and the sensor size of the camera. Just out of curiosity: is this a quiz or does your question have a practical point to it?
Comment: The math https://en.wikipedia.org/wiki/Angle_of_view
Comment: A rough calculation would indicate 1450mm. If a doubling of the focal length doubles the rabbit size then we can divide the width of the image by the width of the rabbit, so 1930 pixels for the image divided by 83 pixels for the rabbit gives a factor of 23.if you want the frame to include 80% of the rabbit then multiply 23 by 1.25, which gives ~29. 50mm x 29 = 1450mm.
Answer: Your rabbit, including ears, takes up roughly 70 vertical pixels out of a total of 1,288 vertical pixels.
80% of 70 is 56 pixels. 56 pixels divided by 1,288 pixels is 1/23 of the image height.
You'd need roughly 23 x 50mm, or 1,150mm, to fill the frame with what 56 vertical pixels is currently showing.
You might as well round it off to 1,200mm, because anyone selling an 1,150mm lens will market it as 1,200mm, anyway.
Comment: @slingeraap Except the question doesn't read that way. It asks to get 80% of the rabbit to fill the frame, not to get the rabbit to fill 80% of the frame.
Comment: Using the arctan formula, it's ~1172mm based on your assumptions. Rounding up seems warranted indeed.
Comment: Small error there: the rabbit needs 70 pixels. In order for it to fill 80% of the frame, the frame should be 125% of 70 pixels, not 80%.
So you'd need a frame of 88 pixels, and consequently you would "only"need a lens of 732 mm.
Comment: @MichaelC: you're right, I see now. It made more sense to me the other way around, so that must have biased me.