Are animals commanded (Bereishit 1:22)?

Question: In two places in parshat Bereishit Gd commands "be fruitful and multiply".  The second place is the familiar commandment directed to humans (Gen 1:28).  In the first place, the same words are used but concerning fish and birds (Gen. 1:22).  Are animals commanded?  If so, in what sense?  If not, how do we interpret Gen. 1:22?
Comment: Similar: http://judaism.stackexchange.com/q/62474
Answer: כב וַיְבָרֶךְ אֹתָם אֱלֹהִים לֵאמֹר פְּרוּ וּרְבוּ וּמִלְאוּ אֶת הַמַּיִם בַּיַּמִּים וְהָעוֹף יִרֶב בָּאָרֶץ:
22 And God blessed them, saying, "Be fruitful and multiply, and fill the waters of the seas, and let the fowl multiply upon the earth."
As you can see, this is not a command but a blessing.
Rav Hirsch points out the difference between אמר and דבר as used here. Part of Rav Hirsch's commentary emphasizes that the blessing gives the (non-free willed) animals the power to be fruitful and multiply unlike the free willed following of a commandment which a human being is capable of. That is why the commandment to a human being uses דבר

... the fulfillment immediately followed the command. Hashem
  blessed the organic living creatures, i.e. He gave them the power of reproduction
  and multiplying, and with this power He gave them at
  the same time the direction and urge for it. For in the unfree living
  organic beings, power and fulfillment are not separated. The power
  itself automatically drives them to the fulfillment of that for which
  Hasem has given them that power.

Rav Hirsch differentiates this from the command in 1:28 and explains the difference between Adam (getting a command) and animals (getting a brachah) because it says
כח וַיְבָרֶךְ אֹתָם אֱלֹהִים וַיֹּאמֶר לָהֶם אֱלֹהִים פְּרוּ וּרְבוּ וּמִלְאוּ אֶת הָאָרֶץ וְכִבְשֻׁהָ וּרְדוּ בִּדְגַת הַיָּם וּבְעוֹף הַשָּׁמַיִם וּבְכָל חַיָּה הָרֹמֶשֶׂת עַל הָאָרֶץ:

He gave them the command to fulfill the mission of mankind on Earth.
  Whereas above, in verse 22 it says וַיְבָרֶךְ אֹתָם אֱלֹהִים לֵאמֹר
  here it says וַיְבָרֶךְ אֹתָם אֱלֹהִים וַיֹּאמֶר There in the unfree
  living creatures, as already remarked thereon, with the giving of the
  blessing, ... the fulfillment of this blessing is already
  automatically given.
Here, in human beings, the blessing, ... is separated from the
  fulfillment i.e. from using this power and ability for the purposes
  for which Hashem intended them. ... That which in animals is a purely
  physical act becomes in Man a free-willed moral act.
Comment: Mankind are similarly blessed and not commanded in verse 28. If there is such a large difference between Davar and Amar, then we would lose out on some commandments later when God uses Davar instead of Amar
Comment: @Aaron I added Rav Hirsch explaining the difference in the two pesukim. I do not have time to give the full quote, but have put in the appropriate segments.

Are animals commanded (Bereishit 1:22)?


Entity getOwner()

Question: In what table does an entity "foo" get its metadata stored? In Drupal 7, there are tables for all the fields for a content type and the node table had some metadata stored, but most data for a content type were in other tables. I think I understand that configuration is what metadata is required for an entity. But I cannot figure out which tables would store an association between node/100 and user/10. Using breakpoints I'm trying to troubleshoot where in the node object this info resides and try to deduce its definitions to backtrack where metadata like author/owner is stored.
Comment: This is a base field referencing the user entity, since D8.7 standardized in a trait [EntityOwnerTrait::ownerBaseFieldDefinitions](https://api.drupal.org/api/drupal/core%21modules%21user%21src%21EntityOwnerTrait.php/function/EntityOwnerTrait%3A%3AownerBaseFieldDefinitions/8.7.x)
Answer: In Drupal 8 all that stuff is stored as YAML files in your config directory.
If you don't have a custom path to that directory it's usually located in sites/default/files/config...... where .. is a long randomly generated hash key.
There you will find config files for all entities and fields and configuration settings.
EDIT: To get a node's asociation with it's author you'll have to look in the node_field_data table, the UID field there is the author's user ID.
Comment: Yes, thank you. Running vendor/bin/drush cex I see the dump of all current config. Searching for a string of either "100" or a partial of the UUID for node/100 ("55b1372d-9ec2-4a4d-b878-") returns no such data. Searching the config table for any mention of this node returns no data. There's something in the db to make the association of an instance of a node with its author, and other node metadata?
Comment: Try to look at my edit

Entity getOwner()


Trying to find author of short story called Man Alone

Question: I'm not certain that is the title but the plot was about a guy who had been modified with machinery equipment to live on Mars. He was a reluctant 'experiment' at first but once he arrived he was "operational" and became perfectly suited to function and turned his back on his creators.
Comment: That's five. Actually four, because Scarff = Budrys.
Comment: @user14111 - My maths apparently leaves something to be desired
Comment: There are six stories on ISFDB called "Man Alone" - William Scarff (1959), Don Berry (1958), Wolcott Gibbs (1932), Algis Budrys (1959) and Drew Arrants (2008). When did you read it and where did you read it?
Answer: It appears that you have slightly mis-remembered the title.  I think you are describing "Man Plus" by Frederik Pohl.  It is the story of an astronaut who undergoes body modifications to enable him to live on Mars.  He was originally the backup astronaut and didn't really want to do it.

The first Earthling reworked into a Martian would be Roger Torraway.
Martian instead of Earthling since everything on him had to be
reworked in order to survive on Mars.  His organic skin is stripped
off and made plastic.  His eyes are replaced by large, buglike red
ones.  He is given wings to gather solar power, not to fly.  All of
which is organized and run by his friend, the computer on his back.
Who was this man? What was his life like? How did he survive the
transformation to become more than human and help us successfully
colonize Mars?


who chooses what gets on, or is taken off the web

Question: A lot of information no longer exists on the Web. Removed!
Who is the one or group to choose what may continue to exist on the Web?
Comment: And this is off topic.
Comment: The person who removed it is (most of the time) the person who created it.
Comment: What?! You do realize it costs money to put something up on the web (not every one runs a website with dydns out of their basement)... No single person controls what gets put on or taken down it is up to the original content owner.
Comment: I feel like this belongs at http://skeptics.stackexchange.com (but it may even be too conspiracy-theory-y for them!).
Answer: There isn't a unified group that oversees all Internet content.  It isn't possible since the Internet is a decentralized global network.
Usually the following entities are responsible for removal of content:

the person who created the content
the people or company hosting the content
a government agency forcing content offline because of a violation of law or regulation
an ISP blocks content because of censorship laws or something similar.
Comment: None the less, history is lost. Knowledge that is taken away,
Answer: Well, it is difficult to make a good  answer to this question because it's so broad, but  for start the answer would be "It depends".
First step in understanding the whole process is to understand who is needed to place information on the Internet.
So you first have regulatory agencies which provide central domain name servers and assign top level domains (such as .com, .org, .co, .uk and so on). Next you have central domain registrars. They can make rules which regulate what kind of information can be stored in sites registered to their domains. After them may be sub-domain registrars who control only a part of the domain.
After that you have regular owners of the domains. They have general control what type of information is stored where. In case of larger organizations, they may have entire marketing teams and web-master teams who actually make sites and pick exact information placed on them. Below them may be users who are authorized to post new content (such is the case here. You can post questions and answers and so on).
Another interesting side is hardware side. The site needs to be physically located somewhere on some computer. The owner of the computer is called host. Some people host their own sites on their own computers while others pay companies to do the hosting. The hosts answer to the government of the country where they are located and that country can enforce its laws on them, so in the end owners of the sites need to abide by those laws too.
So it's basically a very complex system. Not every part works great and not every layer cooperates in harmony with others, so you can have all sorts of problems when putting informations which is in some countries objectionable on the Internet.
For example if a site is registered in country A and hosted in country B, country A may seize control of the domain name even if the information is legally hosted in country B. Same thing can be done with almost anyone on the domain registration chain.  Then again you have the host itself. It can remove data, if the owner of the site breaks the hosting contract or if it is placed under pressure by some other institution or if the computers are physically damaged and so on.
In the end owner of the site can of course remove data too from the site. This can sometimes cause major problems for users especially if the owner is a large corporation and it is difficult to see who is directly responsible for each piece of data. For example I have Acer Aspire 7720G laptop. On Acer's support site, there are links to its drivers, but on the server where the drivers themselves are hosted the drivers have been removed and if I didn't have backups, I could have problems with them.
Answer: Your question is too general but I will try to answer it.
The creator of a website may choose to remove its content if it is still under his control.
Content could also be taken down by the services provider (i.e. Google for Google Sites or Blogger, Facebook for infringing posts, etc) if for some reason you violate their Terms and Conditions


What is the meaning of "auch schon"?

Question: In my textbook I found the phrase "Meine Augen tun auch schon ein bisschen weh". I want to know the meaning of "auch schon" in general and when to use it
Comment: "auch schon" means "aswell". The "auch" part literally means "too"  and the "schon" part means literally "already". Could be used when someone told you their eyes hurt because of some external stimuli (e.g. teargas). And you reply "my eyes have started to hurt aswell". Or when someone remarks something and you think it's obvious, you can reply (sarcastically) "Hast du das auch schon gemerkt?".
Comment: The "auch" does not necessarily mean "too" or "as well". It can also suggest causality. Assume there's tear gas. "Meine Augen tun schon ein bisschen weh." means "They are hurting already.". "Meine Augen tun *auch* schon ein bisschen weh." means "They are hurting already *because of the tear gas*."
Comment: @usr hmm, I think I have seen that being used. But it highly depends on the accentuation and context. "Meine Augen tun *auch* schon ein bisschen weh" doesn't suggest causality. But "Meine Augen tuen auch schon ein bisschen *weh*." might suggest causality.
Comment: @JohannesSchaub-litb I would say it depends on the context what it means. I had no idea that German is such a crazily complicated language.
Answer:
auch = also, too
schon = already

Other parts of speech:

meine Augen = my eyes
tun ... weh = hurt
ein bisschen = a little bit

All together:

My eyes also already hurt a little bit.
Comment: "Auch" doesn't necessarily mean "also", "too". This would require that there's someone else whose eyes hurt. But consider the following context: "Ich sitze seit 10 Stunden am Computer. Meine Augen tun auch schon ein bisschen weh." There is no other person, so the meaning cannot be "also", "too.". It's just a particle that could be dropped altogether.
Comment: @Em1: There is no need for another person, neither in German nor in English: »I am sitting on the computer for 10 hours, and my eyes also already hurt a little bit.« With this sentence you tell, that you suffer from two things: a) sitting 10 hours on the computer, and b) also eyes that hurt.
Comment: I think in German, it's more subtle than that. I have heard "auch" being used as a fill word like @Em1 describes.
Comment: In some cases "auch" can be translated better as "what's more". A problem with "auch" and similar words is that they are used a lot more in German than in English. But usually they are not mere filler words but add some nuance.

What is the meaning of "auch schon"?


What is this succulent/weed growing on my lawn?

Question: We've had it growing in our backyard lawn for a while and the patch gets bigger every year. Its definitely in the succulent family but I can't find any other information on it. We live in West Michigan if it helps. Its very strange- Help internet!
Comment: Stackexchange contributors are located in many countries and to help us all understand your problem better, we appreciate a little extra information such as your physical location (not address, just country/area/city) and if possible a few other details such as the type of soil in your garden, the type of lawn. Great photo though - very clear and helpful! If you're able to provide additional details, please update your original question by clicking the [Edit] button above.
Answer: It's a Sedum variety, common name Stonecrop. As to which one, it's fairly similar to Sedum album 'Coral Carpet', http://www.craigiehallnursery.co.uk/ourshop/prod_2071779-Sedum-album-Coral-Carpet.html, although the colour of yours is duller - that might be due to reduced uv levels through winter. There are many varieties which are similar, but the puzzle is why it's growing in your lawn - stonecrop varieties often have an indefinite spread, so if it had been planted in a border or bed and invaded the lawn, that would explain it.
You should be able to dig it out without too much difficulty, but it is considered an ornamental plant, useful as ground cover in sunny, dry places in the garden; it's only a weed in this case because it's growing where you don't want it to. If it's a large patch, you will need to do some lawn repair after digging it out.
Comment: Thank you very much- that's helpful. It's so weird- it is right in the middle of the lawn. We live in West Michigan :) It sounds like we'll be doing some lawn repair- the patch is about 20+ sq.ft.
Comment: This stuff is expensive in the shops.  I was looking for some as a ground cover and bee magnet but the cost was too prohibitive.
Comment: If the lawn is free draining and mown short _Sedum_ could easily infiltrate, it's a tough plant. I note that the European _S. acre_ is listed as invasive in some parts of Wisconsin and _S. album_ is no weaker growing in my experience, so it may have arrived by seed. Would have said 'Coral carpet' is a bit tentative, especially given how variable _Sedum_ can be.


Is msg.sender.send(msg.value); safe?

Question: Is there any sort of reentrancy attack that could go along with using this line of code in my smart contract?
Comment: Yes, if it's not the last line before returning from the function (i.e., not necessarily "the last line of text", but a line after which the function returns). For example, consider the case where `msg.sender` is the address of a contract whose fallback function calls your function.
Answer: msg.sender is reliably the immediate, innermost sender that invoked the function. It could be another contract, so it's not necessarily the signer that kicked off the transaction. Hopefully the foregoing doesn't confuse the reliability of it. It reliably does what it is supposed to do.
msg.value is reliably the Ether amount sent to the function. It does not include gas, which is a separate issue. In the case of a chain of contracts. it is not the funds the signer sent. It is the funds that arrived in the function. The caller has to go out of their way to forward funds to another contract.
The statement itself will work as expected, and it will send 2,300 gas (the stipend) which is insufficient to launch a reentrance attack. 2,300 is just enough to emit an event, but not enough to update state, and whatever happens in the fallback function, there will be less than 2,300 leftover. The circuit-breaker depends on pricing, not code logic. It is better to rely on sound logic.
The reentrance defense relies on the order you address certain concerns so it doesn't matter how much gas you send or what the receiver does with it. Check out checks-effects-interactions: https://solidity.readthedocs.io/en/v0.4.24/security-considerations.html

Checks: Is this transaction acceptable? Seriously consider
revert/require to "fail hard" in the case of an unacceptable request. It's usually the right thing to do.
Effects: Now, do all of the bookkeeping, state updates, events, etc. optimistically. This puts your house in order before you transfer flow control to an untrusted contract.
Interactions: Finally, interact with call, send or transfer. It ought to be the last thing the function does. If this happens to fail then you need to revert everything you did in step 2. Revert is done automatically for you if you used transfer. The compiler will complain if you do not check the return bool (success?) from send or call.

Reentance attack is possible if those concerns are approached out of order.
Also worth consideration:
send is usually the wrong choice. Consider transfer. If would be equivalent to:
require(msg.sender.send(msg.value)); // silences the unchecked return value complaint
And, why are we doing this? There must be a reason. Suppose only members are allowed to play, and that's why we want to return the money.
require(isMember(msg.sender), "You are not a member."); // fail hard
Since require reverts, the entire transaction must fail for non-members. While there are always exceptions, this is a good default approach.
Hope it helps.

Is msg.sender.send(msg.value); safe?


Black screen after High Sierra update, MacBook Pro w/user-installed SSD

Question: Ran the High Sierra updater, walked away as it ran. Came back after 40 minutes or so to find a black screen. That's it.
Keyboard was backlit, and pressing keys (spacebar, arrows, esc/fn/command/option) don't wake things up. If I leave it alone for a while, the keyboard goes dark, but a key press lights it back up...but still no screen.
It's a late-2011 15" Core i7, 2.2 ghz, with 4gb RAM and a hard drive upgraded from 500gb rotating media to 1tb SSD (Samsung 850 EVO).
(As a side note, my late-2014 Mac Mini updated just fine.)
Any thoughts on how to proceed?
UPDATE: a pal suggested shutting the lid, waiting 30 seconds, then re-opening the lid. That powered it down...somehow. Then I held down the power button till it restarted, and all is (now, thankfully) well. Hope this helps someone out.
Answer: Mikey_S has answered the question on his/her own:

a pal suggested shutting the lid, waiting 30 seconds, then re-opening
  the lid. That powered it down...somehow. Then I held down the power
  button till it restarted, and all is (now, thankfully) well. Hope this
  helps someone out.


Image based adsense site

Question: I got rejected when trying to apply for an adsense account, it said that I'm lacking textual content. Well, that's a real problem. My newly finished site is a image based site with little or no textual content. Even I used Facebook's comment API for the commenting system, which later renders to be an iframe. So it won't even get past the adsense crawler. Users (including me) have uploaded 27 images to the site so far, but I don't think that 1000 images will make any difference. I'm deeply perplexed now and have no idea on how to get my account approved. Any good idea so that I can get my account approved?
Answer: You don't really have many options here; they've already told you exactly what you need to do: find a way to include more text-based content, or move along to another advertising system that works differently.
As you describe things, your site is just fundamentally incompatible with the entire operation of AdSense. It crawls your site's (textual) content to figure out what ads to serve there. If you don't have any, then it can't really work properly.
For whatever it's worth, here's a AdSense forum thread with someone asking a site that apparently got through somehow, though also note the comment about non-standard code.
Comment: Any good ad company recommendation for my site?
Comment: Try a company like http://www.tradedoubler.com/ which can provide advertising in a non-contextual basis.
Comment: You could also add a blog to the site to build your text-based content.
Comment: @VincePettit Unfortunately tradedoubler is only for europe haha
Comment: You could add something like captions for the photo's. A small description of the picture. Add a part of it as alt, add a caption over the image and you've got yourself some simple text :)

Image based adsense site


Custom Report type with User and Case objects

Question: I created a custom report type with User as primary object and Case(Case Owner) as secondary object. I am trying to build a report which gives Cases Count by Agent. Counts has to be the users(from two profiles)and a Queue. But the report is displaying only cases created by Users but not cases assigned to queue. Please let me know the report type i created is correct or not. I could able to query accurate results through soql query.
Answer: Standard 'Cases' type report could give you the case owner - whether user or queue.
Update
Based on your comment, I'd recommend to create a Custom formula field on Case where you could determine your category based on your custom Department picklist field value on User, or by Queue name.
When you use User as a Master object for custom report type, it automatically filtering out Case records owned by queue as it a cross-object field but you want to use only one.
Comment: I have added User object as we have added custom field - Department which is is a picklist to group users with different profiles under one department(Eg. Sales Support Agent and Sales Support Manager belongs to same department.). That is the reason why I have created custom report type. But with Case( owner), i am not able to get user and queue.
Answer: If I understand what you are trying to do, instead of adding the case owner as a secondary object just have the case object alone and add the lookup fields to the record to the page layout. This will allow you to create a case report and include additional fields related to the owner.


Space Ship capable of travelling from Earth to Moon and back

Question: What would be required to have a vehicle like the space shuttle in that it could launch from earth and travel through space and was reusable except that it also possessed the capability to land on the moon and return to earth. I am writing a science fiction novel where this occurs...just need a simplistic theoretical idea to make the journey in the book somewhat plausible even if it's not possible yet.
Comment: If you watch Elon Musks recent BFR presentation he presentes such a veichle, the two stage BFR launches into an eliptical earth orbit where it is refueled by more BFR launches. The BFR first stages all landing. The tankers going back to an earth landing and the refueled spacecraft then landing on the moon and returning to earth without further refuling.
Answer: Being very minimalist you could achieve this trip with the following Delta V's.

LEO with 9.2 km/s Delta V
LLO with 4,04 km/s
Lunar surface 1,7 km/s
Lift to LLO 1,7 km/s
Back to LEO 1,31km/s (without the burn to slow down the craft therefore stressing the heat shield more)

Adding all that up gives us about 18km/s of required Delta V. That however is a very minimalist Delta V budget, absolutely no room for mistakes or non-optimal paths. Not only is that but the launch from earth uses metrics for dense launch systems which is very optimistic. The landing on the moon is also very tight so if distances are judged incorrectly the retrograde burn would waste more fuel. Assuming we managed to solve those two problems the very minimum Delta V would be the mentioned 18Km/s.
Using HydroLox Rockets the highest ISP of chemical rockets ever produced.
At about 450s you would need e^(18/4,5)= ~55 . That means that your rocket would need a craft that could carry 55 times its own weight while inside earth atmosphere with at the very least 1,5 G's of acceleration. The best rockets that can deliver the required acceleration with fuel easier to handle than hydrogen are three times heavier than that and current normal hydrogen rockets are about 6 to 8 times the target weight so rocket fuels are out.
If we use NTR (Thermal Nuclear Rocket) engines with the target specs of project Timberwind and considering that the hydrogen tanks had equivalent mass per volume of the External Shuttle Tank entirely for H2. We would them have about 150 Tons H2, 25 Tons for Tank, 9 tons engines. This is a realistic rocket up to the point where we notice that we ignored all other needed things like navigation, payload fairings, all the wiring, heat shields, landing struts, control structures, Etc. that said the Vac DeltaV is:
DeltaV=1000s*ln(184/34)=1,688*1000s=16,88 Km/s
So the bare minimum weight is not quite slim enough. With a different design things start to look better. The High thrust portions are dealt with by the NTR and Ion engines for Lunar transfer and return. So you would need:
High thrust 9,2+1,7+1,7=12,6 Km/s = 72% weight
And another 12 Km/s for low thrust Lunar Transfer. (for some low thrust maneuvers you need more Delta V)
At 40 Km/s Exhaust speed you would further need=33% weight
Total fuel weight=1-0,28*0,67=0,79
The payload + ion engine weight is limited to 3% (100%-18%-79%=3%)
So we assume 1 % payload and 2 % "engine"
Let's assume a high-power density of 500 W/kg. For every ton of land craft we have 20 kg of solar panels+engine.
10 kw/ton. Modest 50% Efficiency = 40mg exhaust / ton. Total exhausted fuel = 70 kg
1,75 Mega seconds=24 days thrusting for the moon and back (Actual time should be 2 or 3 times higher because the order in witch it was calculated didn't take into account the fuel to burn on the moon. For all other purposes the calculations are correct.)
There are some approximations like 1000 sec is not 10 km/s but 9,82 km/s but the results are pretty accurate in the context they were used.
Conclusion, with a mix of NTR engines and Ion engines, ignoring all other things needed except propulsion (good enough for a book with significant but quite sci-fi improvements on current technology). Or you stop mid way to refuel. Leo before going to moon sound good and with current thecnology should be achievable.
There are of course other technology open cycle that with enough money and a decade we could "easily" make, but releasing nuclear fuel in the atmosphere is not such a good idea.
Comment: Your calculation using HydroLox is missing the use of stages. Theoretically it would be possible with HydroLox using about five or even more stages. But storing liquid HydroLox for the whole trip would be a problem. Boil off losses of fuel should be low.
Comment: Since he talked about a reusable space craft I was going for a Full reusable, single stage and I think I did the math properly. In pratice this would not work with current technology but the math is there to figure i out. I ignored litle problems structural integrity, boil off, reentry shielding, plumming and other stuff a real space craft would need.  Tnks anyway for the coment.
Comment: He wrote about "a vehicle like the space shuttle", so external tanks and boosters are possible. Full reusable was not required, only a reusable vehicle like space shuttle
Comment: @everyone - thanks for your reponses - they are helping me brainstorm the problem. Please keep in mind this isn't "hard" science fiction so I won't be going into much detail and fiction is the operative word although I don't want it to be ridiculous. So far I plan on using solid rocket boosters to achieve escape velocity from earth, and high powered ion propulsion system for space travel and moon landing. I know the escape velocity to leave the moon is much smaller - what would be a good way to obtain the necessary velocity to escape the moon's gravity and return home via ion propulsion?
Comment: I don't think it's realistic to use ion propulsion to lift off from the Moon they don't provide enough thrust. Realistically you need to refill the rocket in LEO and solid rocket engines are not the best choice as they are less efficient than liquid fueled rockets.
Answer: Getting from Earth into space is cheap (for rather large values of cheap...but ti has been shown that a missile (an ASM-135 ASAT) fired from an ordinary fighter airplane (an F-15A "Eagle") can make it into space (and shoot down a satellite there (https://en.wikipedia.org/wiki/ASM-135_ASAT))). Staying in space (achieving orbit) is expensive. Most of the fuel is consumed to bring the fuel into space (and have it stay there).
So...let's try it the other way around.
We need a fuel factory on the moon (or somewhere else near Earth, could be an asteroid or whatever). Getting into space from the moon and staying there (or going to Earth) is frigging cheap. So, if we can produce fuel on the moon, we could establish a cheap shuttle service from moon to Earth. The Moon-Earth-Shuttle won't land on Earth, but it can pick up payload which gets launched from Earth into space. Since it's cheaper to launch moon-sourced fuel into space than Earth-sourced fuel, this Moon-Earth-Shuttle would use this cheap "moon fuel" to brake hard near Earth to pick up the payload and then re-accelerate again for the trip back to the moon. Cheaper that way than to accelerate the payload with "Earth fuel" to get it into a Lower Earth Orbit.
So we will have two spaceships, one Moon-Earth-Shuttle and one Earth-Space-Shuttle.
The Earth-Space-Shuttle could be a conventional design, or maybe a laser-power spaceship. A laser-power spaceship does not need to carry its fuel along with it - the fuel stays on Earth and the energy is "beamed" to the vessel. One of the current designs uses the surrounding air as reaction mass. There are also other designs which carry reaction mass on board.
Note: I have not calculated the "orbital" maneuvers for the payload handover rendezvous. Also not that I have no clue on how to "mine" (produce) fuel on the moon. LOX might not be a natural resource on the moon :-). But some water is there, apparently (https://en.wikipedia.org/wiki/Lunar_water - also check the Ownership paragraph for some legal questions). Then again, using an asteroid as a fuel source could also be an option (https://www.space.com/1526-largest-asteroid-fresh-water-earth.html).
Obviously, the initial setup cost of a fuel factory in space or on the moon would be enormous. And this still does not answer the question why someone would want to travel to the moon (at least now that the space race is over).
Note that the OP specifically didn't ask for a "hard scientific answer", but rather for some inspiration for a "soft" SF novel.
Also note that I interpret the requirement for a reusable spacecraft as the intention to build a regular Earth-Moon shuttle line. Hence my idea about accepting a much higher initial setup cost.
An other idea for launches from the moon was a rail gun (or linear motor), like in this question: Can we use a rail gun on the moon to launch stuff directly to mars?. However, for a "simple" return to Earth, it would probably not make sense to invest into a rail gun/linear motor, since launching from the moon to return to Earth is so cheap anyway.


Why is Lightning referred to as High frequency source?

Question: Lightning strike is categorized as DC because of its electrostatic nature. The negative flash/stroke is found to have 200KA of current with a voltage close to 300KV (cloud to ground). But why is it referred to as a High frequency source, since it does not have a  frequency component?  In an electric circuit diagram will lightning be represented as a voltage source or current source?
Answer: Of course lightning "has a frequency component".  If it didn't have non-zero frequencies, it could never start or would last indefinitely.
Lightning is a huge current pulse over a short time, usually several pulses over a few milliseconds.  But more importantly, the current is started and stopped very abruptly, which by necessity means it has a broad spectrum containing significant high frequency content.
Spark gaps in general are infamous for being broad band frequency sources well into the radio range.  Some early radio transmitters harnesses this by connecting a spark gap to a resonant circuit.  Since the spark gap produced a wide spectrum, it also produced the frequency of the resonance.  However, the other frequencies aren't sufficiently attenuated, so spark gap transmitters are specifically banned in the US (probably most countries).
I think your question really comes down to a unawareness of Fourier analisys.  That would be a good search term to look up additional information.
Comment: Actually, it's worse than that. https://en.wikipedia.org/wiki/Lightning#Re-strike
Answer: According to wikipedia, average duration of a lightning is $30\,\mu s$. If we take a gaussian current splash with $\sigma=30\,\mu s$, its spectrum will be a gaussian with $\sigma_k\approx33\,\text{kHz}$. This doesn't look like DC.
Answer: I'm not sure what's meant by a "gaussian current splash". But per various sources, an individual lightning stroke (ignoring repeat strikes, branching, etc) consists of an essentially instantaneous rise from 0 to perhaps millions of amps, followed by exponential decay with a half-life of around 5 microseconds (although there's quite a lot of variance in that number depending on where you read). I made up some data like that and ran it through an FFT. The answer was that you do get quite a lot of DC and low frequency AC, but there's also significant energy put out in the 5 KHz and above range.
Answer: Your base assumptions are incorrect. Lightning voltage has a rise time of 8 - 10 uS and a decay of 20 - 350 uS. The peak current for naturally occurring lighting is around 200 kA. Take a look at IEEE C62.72 and IEC 62305.


Why not directly confess our sins to God?

Question: Why should we confess our sins to the Catholic priest, when God is everywhere and He listens to us every time? Is this the only way to be forgiven? What is the assurance that sins are forgiven?
Comment: Probably a duplicate: [How do Catholics justify confessing to a priest?](http://christianity.stackexchange.com/questions/6965/how-do-catholics-justify-confessing-to-a-priest)
Comment: Except that it's tagged westminister-confession... can you please edit the question to explain exactly who you're asking, and what sections of the Westminster Confession are relevant?
Comment: You are aware the the Bible commands Christians to confess their sins to other Christians, not just to God, aren't you?
Comment: Again this question needs a tighter scope because it's collecting Catholic and Orthodox answers. But I half expect that the OP won't return...
Comment: Whose views are you looking to learn about here? It seems like you are raising a Protestant objection to Catholic doctrine, but this site isn't the place to resolve which is correct. If you specify exactly whose views you are interested in understanding better we might be able to handle this. Can you [edit] with that information?
Comment: sorry for making my question blurred. It is in Catholic view.
Comment: @Ragnarok so is this a duplicate of [How do Catholics justify confessing to a priest?](http://christianity.stackexchange.com/questions/6965/how-do-catholics-justify-confessing-to-a-priest)?
Comment: probably yes. It answers some questions.
Answer: Since the question is about confession to a priest, the answer would rely upon the teachings of the Catholic Church. As such the best place to find the answer about why Catholics would confess to a priest are found in the Catechism of the Catholic Church.
The particular paragraphs that cover this are under the heading "Ministry of This Sacrament" in regards to the Sacrament of Reconciliation. Here it is clarified that, in keeping with the teachings of the Catholic Church, Christ "entrusted to his apostles the ministry of reconciliations, bishops who are their successors, and priests, the bishops' collaborators, continue to exercise this ministry." This is why Catholics confess to a priest.
To answer the second part of the question it is important to understand most fully what confession is according to the teaching of the Catholic Church. The purpose of confession is to reconcile one back to God where sin has severed or separated one from God to any degree. A practicing Catholic would not deny the truth that confession could be made directly to God or to Christ but would argue that due to our subjective nature in regards to self, a more perfect confession could be made when an Examination of Conscience is done and confession is made to a priest who, according to the Catechism, "is fulfilling the ministry of the Good Shepherd who seeks the lost sheep, of the Good Samaritan who binds up wounds, of the Father who awaits the prodigal son and welcomes him on his return, and of the just and impartial judge whose judgment is both just and merciful. The priest is the sign and the instrument of God's merciful love for the sinner."
Further, as the Catechism states, once confession to a priest has been accomplished with a "contrite heart and religious disposition, reconciliation is usually followed by peace and serenity of conscience with strong spiritual consolation."
And while this becomes a personal experience and difficult to justify, nonetheless I believe it is worth saying that people who do participate in confession with a contrite heart and belief in the teachings of the Catholic Church will attest to the power of the sacrament.


Probability for label correctness in semi-supervised learning

Question: I am aware of the existence of semi-supervised learning approaches, such as the Ladder Network, where only a subset of the data is labeled. Are there any methods or papers which consider correctness probabilities for the labels of that training data subset? That is, some labels may be correct with 100% probability, while others may have only 70% or 45% probability of being correct. Any links to papers or work in this direction are highly appreciated.
Comment: Just adjust the loss function? For example, with a binary classifier a probability of $p$ in one class induces a probability of $1-p$ on the other. In a multiclass setting you have to decide how to apportion the complement (equally?). With regression losses it's just a multiplicative coefficient.
Comment: Would simply adjusting the target work? If the probability of correctness is 40%, you could assume that the other classes have in sum a probability of 60%. Hence your target would not be 1,0,0,0 but 0.4,0.2,0.2,0.2, for example.
Answer: I do not know any papers, I would be greatly appreciated if someone would link some.
In my case, I always test by un-labelling my already known labelled Data by using a "traditional" 67% - 33% (train - test) split and checking how the labelling performs in various metrics (Accuracy, Logloss, etc.).
Moreover, there are various categories of Semi-Supervised Learning. For instance, if you would use Active Learning (pool based approach, includes incrementally sample/s each time), you could view how the performance ranges.
Finally, you may use as well Cross-Validation in the same sense for hyper parameter tuning for your Semi-Supervised Learning algorithm. All in all, in my perspective Semi-Supervised Learning, has a lot yet to offer and your question may be rather more domain, data specific and visualsing the Data and Clustering may give you new insights.


Am I allowed to use a real life celebrity in a game?

Question: In previous questions many users asked whether or not an athlete can be used in a game. Yet the answer was no due to multiple copyright their images and names had. However anyone can use a politician's name and physical appearance due to the fact that they are "public figures" (example: Obama). In this case, I want to use famous game developers such as Kojima and Gabe Newell in a game. Am I allowed to use them? or should I make references to them using distinct names (I.E. Lord Gaben). How can I find out whether or not a person is a "public figure" and if their appearance/name is protected?.
Comment: Most users on this site (including myself) are not lawyers and can't offer you legal advice — you should consult a lawyer to be sure. General guidance I've been told is that fair use (eg. for parody of a public figure) is a *defence*, not an automatic exemption. If someone feels that you are profiting from using their likeness without permission, or that you are defaming them, they can pursue legal action against you. You would then need to defend in court your claim that your work constitutes fair use, which may be quite expensive.
Comment: I'm voting to close this question as off-topic because it's not about game development.
Comment: Check http://law.stackexchange.com
Comment: you can read about that case also: http://www.gamespot.com/articles/gta-5-lindsay-lohan-lawsuit-thrown-out/1100-6443249/
Comment: Parodying celebrities might be covered under "freedom of speech". But there were various decisions of courts all over the world which found that video games do not always have the same rights of speech and expression as other media.
Answer: Generally speaking, personality rights prevent you from using another's name or likeness without permission.
There are exceptions, especially depending on your jurisdiction. The United States is particularly involved, as I recall, because many states have laws concerning publicity which may all differ slightly. It is best to talk with a lawyer familiar in the matter about your specific intent.
To determine who should be contacted to negotiate for a license to somebody's personality rights you should also consult a lawyer.
Comment: Satire laws may be applicable depending on how the image is used.
Answer: The consequences of using a celebrity likeness can lead to severe legal repercussions as Todd McFarlane could tell you.

In the Spawn comic book series, Todd McFarlane created a mob enforcer
  character named Antonio "Tony Twist" Twistelli,[2] who McFarlane
  acknowledged was named after Tony Twist. Twist won a $15 million
  verdict in 2004 when a St. Louis, Missouri jury found Todd McFarlane
  Productions had profited from Twist's likeness.[3] The verdict was
  upheld after two appeals in June 2006.[4] In 2007, Twist and McFarlane
  settled the lawsuit out of court for $5 million.[5][6]

Long story short - generally you cannot use celebrity likenesses for living figures. For dead, historical personages it's another story but still not 100% safe.
For living figures you can pretty much forget it. You can claim parody but only if the whole game is obvious parody and it helps a great deal if you are known as a comedic personality of some kind. Even so, nothing stops you from being sued on those grounds even if you are in the right and the legal bills could be quite expensive.
For historical figures you are generally OK but there still may be restrictions so it could be worth speaking to a lawyer, and anything touching on properties or companies that they may have been involved with is completely unprotected.


How to handle single trial ERP (P300)

Question: I am learning to work with EEG data in young and elderly subjects. The goal is to find differences in P300 (amplitude & latency) between both age groups during learning. I analyzed the data based on Grand Averages of both groups. As a confirmatory analysis I've tried to find the P300 peak for each subject individually and I performed analysis based on this peaks. Now I am interested in the variability in P300 latency in each trial, especially in elderly subjects, as the decreased P300 amplitude might be partially explained by averaging of more variable peaks. The single trial data looks very noisy and based on the fixed time window for searching P300 peaks, I am getting very different latencies for each trial. The topographies of single trial data also does not help - some looks ok, but others are just noise. Does someone know, how to handle P300 in single trial EEG data? Are classification methods for BCI going to work for this project?
Comment: Looks related to: [What are other methods for adjusting latency jitter in event-related potentials (ERPs) (P300 in particular) besides Woody filter and peak-picking?](https://psychology.stackexchange.com/q/15801/7001), [What are some good references for preprocessing and analysis of the P300 response from EEG data in Python?](https://psychology.stackexchange.com/q/9402/7001), [How do you form a rationale to justify choice of time windows in ERP analysis?](https://psychology.stackexchange.com/q/15997/7001)
Answer: I remember trying using single-epoch measurements with electroretinogram (ERG) recordings. Basically, ERG responses are electrical potential recordings from the neural activity in the retina. ERGs are usually also obtained using ensemble averages.
The single-sweep ERG amplitude measures were, as expected, also really messy due to random noise and eye movement artifacts that are normally averaged out when using ensemble averages. However, when using all 250 available individual epochs I had at the time, I could still show that ERG amplitudes slowly declined along the duration of the recording. So I took advantage of all available recordings by plotting all available amplitudes against time and performing linear regression. Linear regression is a particularly robust statistical method when a lot of data is available.
In your case, where you basically wish to do an analysis of variance on  populations of people, I would try to pool all the data available per subject and determine the standard deviation, or a related variance parameter. Then doing that for all 20 normal subjects will yield a collection of variabilities. This could then be compared to the older population. I can't advice you on the most appropriate statistical test unfortunately, but for a starters you can simply plot the 2 point clouds and compare them visually. If it looks promising, you can do a t-test (which is likely not the most appropriate test, but it will give you a fair indication). If it all looks promising, you have to find a proper analysis of variance to compare the two.

How to handle single trial ERP (P300)


Why was Joab concerned about taking a census

Question: I've read many commentaries on 2 Samuel 24:3 that debate several reasons why the census was sinful but none of them address Joab's reason for asking.  Joab was a gifted military commander and loyal to David, but he was not a moral man.  He killed Abner, Uriah, and Amasa, none of them for military advance but for various and questionable reasons.  His concerns seem directed toward military or personal gain, and I see nothing to indicate humility.  With no indication of him acknowledging God for much of anything, why would he now be concerned about offending God.  My question is not, what was the offense, but what would generate Joab's concern.  Once that question is satisfied, the context of the verse might become clear.
Answer: Joab believed in God's power. He was not an idol worshiper.

2 Samuel 2:27
Joab answered, "As surely as God lives, if you had not spoken, the men would have continued pursuing them until morning."

2 Samuel 10:11 Joab said, "If the Arameans are too strong for me, then you are to come to my rescue; but if the Ammonites are too strong for you, then I will come to rescue you. 12Be strong, and let us fight bravely for our people and the cities of our God. The Lord will do what is good in his sight."

Uriah respected him.

2 Samuel 11:11 Uriah said to David, "The ark and Israel and Judah are staying in tents, and my commander Joab and my lord's men are camped in the open country. How could I go to my house to eat and drink and make love to my wife? As surely as you live, I will not do such a thing!"

Joab is a complex character.
Comment: Not buying it Tony.  Just because someone uses a little God talk doesn't mean he's a believer.  Actions speak louder than words.   He did bad things with no sign of repentance, as did David.  I don't see anything in his life that would make me put stock in him as a man of God.  As for Uriah (who he murdered), he respected him as a military commander.  If it had been Uriah speaking about spiritual issues I would have no questions.  No, Joab was not a man to concern himself with spiritual affairs.  Something is missing here.
Comment: I've made modification.
Comment: But that's my point.  I don't think he worshiped anything but himself.
Comment: You could be right.
Comment: Thanks for your input Tony.  It's a tough question.
Comment: Well Tony, it seems you were more right than I.  I've been told that I'm trying to keep everything black and white, and that is not the case here.  I think Joab's commitment was nowhere as dedicated as David's, and that he had serious flaws, but still had a foundation in faith.  Thanks again Tony.
Comment: You're welcome. We are here to help each other out.


New to WordPress - How viable is it as a CMS for a small business website?

Question: I know the huge community of people behind WordPress has pushed it towards full-blown CMS territory over the past couple years, but I'm still unclear as to what extent. Would it be a good option to handle something like a small biz website with simple shopping cart for example?
Comment: edited your title to make it un-duplicate
Answer: Yes, you can use a spanner to bang in screws if you need to, but you might be better reconsidering.
WordPress may well be capable of running a small website with a shopping cart, and that's probably useful for people who have grown a blog up and are branching out into sales.
But why would you choose a blogging platform for your CMS when there are perfectly good CMS systems that target that role?
Answer: That depends on how small the site is and your intentions; Wordpress is perfectly fine as a cms. If you want a fairly simple site or need to have it moderated by non-techies, its perfect. Wordpress has amassed a huge amount of plugins, taking it from a blog engine to an entire platform. Here's a very rough power vs simplicity scale:
<code>easiest to use

ascii art
microsoft paint
wordpress
joomla
drupal
self written cms
Tapping out your own html in binary on a telegraph key for each HTTP request

most powerful
</code>
Its advisable to use the simplest one that will fit your needs for a long time.
Answer: Something to consider—something I've come to notice, at least—is the savvy-ness or level of familiarity the client may have with WordPress. Directly related to it's growth is it's saturation. It's likely that whomever is in charge of managing the sites content has spent some time with WordPress and would be more effective continuing with it.
That said, from what little I've read about WordPress 3, one of the biggest hurdles to clear, custom post/content-types, is present in the core. To what extent, I'm not sure. Probably better to leave that in the hands of a diehard WordPress dev.
It's certainly true that there are dedicated CMS that pack more of this, or more of that, but don't discount the value of experience. The right tool for the job needs to be the right tool for the job.


Long term career trajectories of quants

Question: Every year a place like Goldman Sachs hires dozens of new strategists (quants) and the same can be said about many other firms. Some of those quants become managing directors and are set for life. But what is a typical career trajectory for a quant like? Does it depend on whether a person has a PhD or not? Even as a VP in NYC you do not really become a high net worth individual, even though you can probably afford a decent life there, so I am curious what happens to most of these people that enter the industry but are not quite in the top 1% that earns the big bucks.
Answer: More a comment than a proper answer, with low rep I can't comment. By the way, I would say that a PhD isn't a requirement in order to do a quant job - look at Citadel, for example: most of their hires don't have a PhD. What they do have, indeed, is the capability to formulate well-posed problems, and to deal even with ill posed ones.

Long term career trajectories of quants


How are topological qubits encoded in the Majorana-fermion-based platform for quantum computing?

Question: Where is "the two level system" of a topological qubit encoded in the Majorana-fermion-based platform of quantum computing?
If the Hamiltonian in a topological quantum field theory is absent (H=0), then what dictates the evolution of a topological system in the circuit model of quantum computation?
Answer: There are many proposals for using Majorana zero modes to encode a qubit; one of the most popular is called the hexon, discussed in this paper: https://arxiv.org/pdf/1610.05289.pdf.
The main idea here is that a one-dimensional topological superconductor hosts Majorana zero modes at its ends.  Two Majorana modes combine into a Dirac fermion, so the ground state is doubly degenerate; either the fermion built from the two Majoranas at the ends is occupied or unoccupied.  Having $2N$ Majorana zero modes gives a Hilbert space of dimension $2^N$.  The architectures discussed in many of these papers are variants on this concept designed to protect the system from unwanted effects like quasiparticle poisoning.
So the qubits in the Majorana models consist of occupying or deoccupying the fermions created by these Majorana zero modes.  However, the Hamiltonian is not $0$ -- we're not dealing with a TQFT, we're dealing with a condensed matter system.  To implement a quantum circuit we perform an adiabatic evolution of the Hamiltonian, taking it along some closed path in parameter space.  While the Hamiltonian returns to its original form, the states evolve into one another.  If the zero modes are kept far apart during this evolution, this evolution is topologically protected; it's a quantum gate.
If we did want to use TQFT language, you would consider your surface punctured with several holes; these holes are defects which bind the zero modes.  Protected operations then generate a representation of the braid group.


Is there a way to bring a loaf of bread that's gone dry, back to life?

Question: It seems that some of the whole grain loafs seem to dry out very quickly, even stored in a plastic bag - if it hasn't started to turn green, is there a way to restore some of the life back into them?
Comment: I live in a very humid climate. The idea of a loaf that is capable of going dry without growing mold makes me really jealous!
Comment: That's one of downsides of NYC - It can happen in 1 day :>)
Answer: Yes. Throw it in the oven on about 200 F for 20 minutes or so. The staling process is called retrogradation, and reheating can reverse it to some degree.
Comment: I do this on a higher heat, say 300-350, and also wet the outside of the bread with water until lightly damp but not soggy.  On that heat it only takes 5-10 minutes and gets pretty good results.
Comment: How much of a degree? And does it work if you reheat for shorter amounts of time?
Comment: You basically want to warm it through, so the time will depend on the thickness. You can also cut slices and very lightly toast them for faster action.
Comment: nice... i'll be using that next time
Comment: Adding a stick of celery inside the plastic container with the bread - has anyone tried that?
Answer: It depends.  If you need it to soften up for just a little while you can throw it in the mircowave for about 10-15 seconds.  And by a little while, I mean the time it takes to make and eat a sandwich.  Other than that, you can use the bread for breadcrumbs or croutons.  Also, dry bread makes the best french toast you will ever have. Basically, you can't turn back time on a loaf but you can make it last longer by freezing it and thawing a slice at a time.
Comment: Microwave is not ideal because it heats the water faster than the starch, tending to cause the bread to steam and actually lose moisture. It will make it seem less stale for a minute, but as soon as it cools down it may actually be worse.
Comment: thus the little while caveat :)
Answer: I have to disagree with the simple reheating method. Bread goes stale through a loss of moisture. Applying dry heat simply doesn't do much beneficial besides toast your stale bread.
Put the bread in a brown paper bag, dampen the top of the bag with water, and then microwave for a few seconds.
Comment: That's not accurate. Yes, some moisture is lost to the outside world, but most of the staling is the starch degelatinization, and reheating above the gelatinization temperature allows it to soften. You can read a ton about it in McGee, or here is a summary on wikipedia: http://en.wikipedia.org/wiki/Staling
Comment: @Michael, @hobodave - I find that this technique works extremely well.  I haven't checked up on how bread goes stale lately (but thanks for the link), but it does seem to help to add moisture.
Answer: Cut it up and toast to make croûtons, or crumble into bread crumbs. Your bread will enjoy new life in a salad or other dish.
If your bread is coming pre-sliced and drying out quickly, try buying unsliced loaves and slicing it as you need it. It's a bit more work, but your bread will taste fresher longer (and as a bonus, you get to decide on the thickness you want).


Do your +1's affect your own Google results?

Question: Your Google plus connections' +1s affect your own Google results. But how about your +1s?  If you +1 a site, will it affect your own Google results? For example, if you +1 Stack Exchange, will Stack Exchange sites be affected in your own Google results?
Answer: There are two different types of Google Results now:

Personalized Results
Hide Personalized Results

From Google's Help Page:

You have to be signed in to a Google Account  to get all of the
  features of personal results. Here's how Google personalizes your
  results when you're signed in:

Google products: Search for publicly and privately shared content
  visible to you, like your Google+ (and Picasa) photos and Google+
  posts from your friends.
Social Search: Discover relevant images and
  pages shared by people in your Google+ circles and by suggested
  connections.
Web History: Get customized results based on your past
  search activity on Google, such as searches you've done or results
  you've clicked. Learn more about Web History
Profiles in search: When
  you search for a friend's name, you might see a link to the relevant
  Google+ profile in the list of autocomplete predictions. With personal
  results, you're more likely to see your friend John's profile than
  some John you've never met. Learn more about profiles in search

You can turn these on and off by toggling the following buttons on the search results page (you need to be logged in to see these buttons)

The button on the left is for personalized searches (turned off in this example). The button on the right is for non-personalized searches and your results won't be based on the items above.
So yes, +1s from your Google+ connections will skew results when you have personalized search turned on. Also, +1s from yourself affect search results on the personalized side.
You can also set your preference on the search settings page. This will only make the settings applicable to the browser you're using as it's a cookie setting and not account specific.
Comment: I added a second sentence in the 2nd to last paragraph regarding that because I noticed that I had originally posted the answer without actually answering it.
Comment: That's not what the OP asked. He's asking about **your** +1s, not the ones from your connections.
Answer: Well, in theory they seem like they should but currently, i would say no.
Let's say you search for something, like this page by searching the title "Do your +1's affect your own Google results?". This page ranks 1st. if you +1 it (using a chrome extension as I have), the page will show up on my g+ list of +1s. Now that I have +1 this page, if i again search the same terms, I will again get this page as the first result. If I have it set to show personal results, the result will show that i +1ed it.
This is the most important part: If I then show personal results by clicking "See all results" at the top, instead of getting my +1ed result, I get results from ppl in my circles. the actual page is nowhere to be found.
My conclusion from this experiment is that, your search results will not be affected by your +1. However, you will be made aware if you come across your +1 among your normal results. There's obviously more intricacies to the search results but I won't get into that here.
1. +1 a site will not automatically bring it to a higher ranking in your search results than if you had not +1 in the first place.
2. you do not see your +1s in you personal personal results (the results that are like "170 personal results" as opposed to "76,000,000 other results")


How can I change my profile photo?

Question: How can I change my profile photo on Ask Ubuntu?
Comment: @Takkat AskUbuntu (directly below where you type your comment) says "Comments are used to ask for clarification or to point out problems in the post".  So, to "point out a problem IN your post", your comment is clearly not asking for clarification, and miscategorization isn't exactly a "problem in the post" is it?  I see no grammar issues, spelling is spot on, and the question itself is very concise and clear.  clicking your link blindly takes me to a 404 page, so i can't even investigate why this question "should be asked in (Meta) .... ".  I'm sorry, but your comment is utterly not helpful.
Answer: Go to your profile page (You can access it by clicking your name at the top of the screen) click the edit link to edit your profile, then select change picture
Comment: I did all that.  Problem is, I get back "Request returned an error: [error] | Close".   Try finding a solution on google for that!  :p  I tried, for a while.  I keep getting hits on how to change my dang windows wallpaper, or my microsoft account profile picture, or whatever.  I guess i don't know how to speak google-ese
Answer: Reuben is completely right, however alternatively just go to gravatar.com - this is where Ask Ubuntu gets your profile picture from (it is based on your email address).
Comment: I gotta create an account at another site to get my picture on this site to change?  That's a problem, because, i don't wanna make an account at some other site.  I'm here...not there.
Answer: Your profile photo is based on your email address and is pulled from the free Profile Hosting site Gravatar If you don't already have an account there, sign up with the email address used on Ask Ubuntu (You can add multiple email addresses, and have multiple "profile images" setup). Upload the profile image you'd like to use for Ask Ubuntu then wait an hour or two for the cache to update.

How can I change my profile photo?


Solving the recurrence $T(n)=T(n−1)/T(n−2)$

Question: How can I solve this?
I saw Solving the recurrence $T(n)=T(n-1)*T(n-2)$ but I don't know how I can apply it to $T(n)=T(n-1)/T(n-2)$?
Comment: Possible duplicate of [Solving or approximating recurrence relations for sequences of numbers](https://cs.stackexchange.com/questions/2789/solving-or-approximating-recurrence-relations-for-sequences-of-numbers)
Comment: What are initial values: $T(0)=?, T(1)=?$
Comment: I just have the equation and no initial values...
Answer: Then assume $T(0) = a, T(1)=b$ such as $a \neq 0$ and $b \neq 0$.
You could write down first few terms and deduce the pattern
$$T(0)= a$$
$$T(1)= b$$
$$T(2)= \frac{T(1)}{T(0)} = \frac{b}{a}$$
$$T(3)= \frac{T(2)}{T(1)} = \frac{b/a}{b} = \frac{1}{a}$$
$$T(4)= \frac{T(3)}{T(2)} = \frac{1/a}{b/a} = \frac{1}{b}$$
$$T(5)= \frac{T(4)}{T(3)} = \frac{1/b}{1/a} = \frac{a}{b}$$
$$T(6)= \frac{T(5)}{T(4)} = \frac{a/b}{1/b} = a = T(0)$$
$$T(7)= \frac{T(6)}{T(5)} = \frac{a}{a/b} = b = T(1)$$
$$...$$
Thus the values of $T(n)$ repeat with period of $6$.
Answer: If you are dealing with a recurrence for which you have no idea how to attempt the solution, it is always a good idea to try working out the first few terms by hand (or using software such as Excel). If you try this, the solution for this recurrence will probably be quite obvious...
Comment: I tried this. Took me exactly 12 seconds to set up a spreadsheet that made the solution shown by fade2black absolutely obvious.


Majorana Mass For Neutrinos In Standard Model

Question: Neutrinos cannot have Dirac masses because there are no $SU(2)_L$ singlet right-handed neutrinos in the Standard Model (SM). But can neutrinos be given Majorana masses in the SM? I heard that Majorana mass term cannot be included for neutrinos in the $SU(2)_L\times U(1)_Y$ SM without any modification or extension. Why is that?
Comment: There are extensions of the SM - new Higgs fields, which generates both of Dirac and Majorana masses. For examples, one of the most popular extension is called see-saw mechanism.
Answer: Yes, they can via a dimension 5 operator that contains two Higgs doublets and two lepton doublets.
This is sometimes called Weinberg operator, it violates lepton number conservation and it was introduced in this work http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.43.1566 .
Since the mass comes from an higher dimensional operator (i.e. an operator whose scaling dimension is bigger than the number of space-time dimensions, also called irrelevant), by dimensional analysis it must enter the action suppressed by a scale, call it $\Lambda$. Substituting the Higgs VEV in the operator, you get that the resulting Majorana mass is of order of the (VEV)$^2$ divided by $\Lambda$.
The meaning of the scale $\Lambda$ is that the operator gets generated by some new physics which resides at that scale (think about the four-fermions weak interaction suppressed by the scale $M_W$).
Using the existing bounds to estimate the mass as 0.1 eV, and taking VEV $\approx 100\,GeV$ you will find that $\Lambda \approx 10^{14} GeV$, which is nicely close (on log scale) to the Grand Unification scale. Nevertheless you have to keep in mind that the operator could be generated with a small dimensionless coefficient, and that could change the estimate.
Comment: Why Majorana mass term cannot be included for neutrinos in the $SU(2)_L\times U(1)_Y$ standard model without any modification?
Comment: Because there is no right-handed (rh) neutrino in the SM. Take the quarks: there's an SU(2)-doublet of lh fields, and two rh SU(2)-singlets, up and down. For the leptons, instead there's the SU(2)-doublet with the l-component of the electron and the lh neutrino, and you have an SU(2) singlet right-component of the electron, but no rh neutrino. If you want you can extend the Standard Model by adding such field. It turns out it would be neutral under the whole gauge group. As a result, you can give it an arbitrarily large Majorana mass. This is one possible way to generate the Weinberg operator
Answer: Lets analyse the Majorana condition and the Majorana mass term.
A massive Majorana neutrino $\chi_j$ (a Majorana spin $1/2$ fermion) having mass $m_j>0$ can be described in a local quantum field theory (eg. the standard model) by a four component spin $1/2$ field $\chi_j(x)$ which satisfies the Dirac equation and the Majorana condition which reads:
$$
C(\overline{\chi_j}(x))^T=\eta_k\chi_j, \text{  where    }|\eta_k|^2=1
$$
$C$ is the charge conjugation matrix, $C^{-1}\gamma_{\alpha}C=-(\gamma_{\alpha})^T$ $(C^T=-C,C^{-1}=C^{\dagger})$ and $\eta_k$ is a generic unphysical phase. The Majorana condition is invariant under proper Lorentz transformation.  It reduces by a factor of 2 the number of independent components in $\chi_j (x)$.
Notice that the Majorana condition is invariant a global $U(1)$ transformation of the field $\chi_j(x)$ (carrying a $U(1)$ charge $Q$): $\chi_j(x)\to e^{i\alpha Q} \chi_j(x)$ iff $Q=0$. Therefore:
$\chi_j(x)$ cannot carry nonzero additive quantum numbers (e.g. lepton charge)
Given this let us now construct mass terms.  In the absence of RH singlet neutrino fields in the theory (which is the case in the Standard model), the flavour neutrinos and antineutrinos $\nu_l$ and $\bar{\nu}_l,l=e,\mu,\tau$ can have a mass term of the Majorana type given by :
$$
\mathcal{L}_M^{\nu}(x)=-\frac{1}{2}\overline{\nu^c_{l'R}}(x)M_{l'l}\nu_{lL}(x)+h.c., \nu^c_{l'R}\equiv C(\overline{\nu_{l'L}}(x))^T,
$$
Where $M$ is a general $3\times 3$ complex matrix. Now coming to your question: Is this mass term $SU(2)_L\times U(1)_Y$ invariant? The answer is clearly NO!  It is not invariant under the weak isospin symmetry, and it changes the weak hypercharge by two units (the hypercharge of all the SM neutrinos is $-1$ which implies that this mass term has a total $U(1)_Y$ charge $-2$). Therefore we need to generate this term via. a Higgs mechanism (as for the Dirac mass term for the electron) or higher loop correction to the SM Lagrangian or possibly some beyond the standard model process.
In conclusion the Standard Model (which does not include RH singlet neutrino fields and contains only the usual Higgs doublet), there is no way to give (Majorana) mass to the neutrinos if fermion (Lepton) number is conserved. Massive Majorana neutrinos appear in theories with no conserved additive quantum number, and more specifically, in which the total lepton charge L is not conserved and changes by two units.
However if you consider Standard model as an effective field theory then there is possibility to generate the above mass term via. higher dimensional operators (which is the context of the previous answer!)
Answer: The important point is the fact that such a mass term breaks the gauge symmetry (Edit: I am assming that you want to build the Majorana mass term using SM available fields -- no extension considered -- of which there is only $\nu_L$). Namely, the desired term is (one generation suffices):
$$\frac{1}{2}\,M\, \nu_L^T \,\mathcal{C}^\dagger\,\nu_L\, +\, \textrm{H.c.}$$
Now, for this term to respect the U(1) part of the gauge symmetry, the total hypercharge must be zero (it is not, as Orbifold pointed out).
Moreover, as far as the SU(2) part is concerned, $\nu_L$ is part of a doublet. So, if your theory is invariant under that symmetry, you should be able to rotate the doublet $(\nu_L,\ell_L)$ under SU(2) with impunity, i.e. without changing the Lagrangian. Here, $\ell_L$ denotes a charged lepton. Clearly, a nontrivial SU(2) rotation would mix both $\nu_L$ and $\ell_L$ fields and the term/Lagrangian is not kept the same/invariant.
Recommended reading: beginning of section 6.4 of C. Giunti and C. Kim's 'Fundamentals of Neutrino Physics and Astrophysics' (Oxford, 2007).


Cannot install http-server on windows

Question: I've just installed node js from the msi installer. I get this error when i run "npm install http-server –g":
<code>C:\dev\workspace_professional_web_development>npm install http-server –g
npm ERR! addLocal Could not install C:\dev\workspace_professional_web_development\–g
npm ERR! Windows_NT 6.1.7601
npm ERR! argv "C:\\Program Files\\nodejs\\node.exe" "C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js" "install" "http-server" "–g"
npm ERR! node v4.2.1
npm ERR! npm  v2.14.7
npm ERR! path C:\dev\workspace_professional_web_development\–g
npm ERR! code ENOENT
npm ERR! errno -4058
npm ERR! syscall open

npm ERR! enoent ENOENT: no such file or directory, open 'C:\dev\workspace_professional_web_development\–g'
npm ERR! enoent This is most likely not a problem with npm itself
npm ERR! enoent and is related to npm not being able to find a file.
npm ERR! enoent
</code>
Is this a bug or is there something wrong with my setup?
Comment: I changed the command to "npm install -g http-server" and it worked. Doh!
Answer: The '–' you're using is incorrect and the source of your error. It appears to be an EM DASH rather than a hyphen '-'
Note that you can tell the difference visually between the two:
– -
Likely it's a copy&paste error from the website or something similar

Cannot install http-server on windows


memory footprint of 4k monitor on 2018 13" Iris 655

Question: I'm thinking of getting a 2018 MBP 13" to connect two 4k displays simultaneously.  I assume that once that happens, the system memory footprint is going to increase in order to buffer these displays, reducing the amount of unswapped/uncompressed RAM I have available for other tasks.  Please contribute with practical measurements of memory usage before and after plugging in the extra 4k display.
Comment: See this related [answer](https://apple.stackexchange.com/a/283602/119271)
Answer: There's not really any significant amount of extra main memory usage for buffers due to having dual 4k-displays.
Indirectly the total main memory usage might increase because some will tend to run more programs at the same time, have more windows and documents open at the same time, etc. - and that will lead to higher main memory usage.
It is correct that the Intel Iris Plus 655 in the MBP uses main memory for its video memory (i.e. up to 1.5 GB of main memory is shared between the CPU and the GPU). However, it is not actually a specific process using more memory in Activity Monitor, but rather a case that there's less main memory available in total.
The size of that extra memory usage for buffers is so little that it is not really noticeable in common usage. For example a video buffer for a 4k display will take up something like 32 MB of memory. That's less than half a percent of even the 8 GB on the MBP with the least amount of RAM.
Again, the indirect usage might be bigger, because you might be loading up more advanced games than you would have done with the extra monitors - and they might use up much more video ram (for textures, etc.) than just the buffers themselves.
Comment: Wow...  No to this!  The Iris Plus allocates up to 1.5GB of system memory to be used as VRAM.  There's no way it only uses 32MB of RAM.  In fact, this [software engineer](https://danielpocock.com/how-much-video-ram-for-a-4k-monitor) finds that you need the full 1.5 for just day-to-day tasks when using a 4K display.
Comment: I worded my responsible specifically to answer the question about the frame buffers, which is what was asked about. And yes, I know that the Iris Plus can allocate up to 1.5 GB of system memory - but only a very small part of that is used for frame buffers.
Comment: The question was about *memory footprint* (meaning of main system memory).  No where did the OP ask about frame buffers.
Comment: Call them display buffers, frame buffers or whatever you will - the original question asks how large the system memory footprint is for buffering the additional displays. Please contribute with practical measurements of memory usage before and after plugging in the extra 4k display (and no other changes) - and these can be added to the answer.
Comment: @jksoegaard, thanks for staying on topic.  as you suggest, the OP has been edited to make further data relevant


How can Formless Brahman create this universe?

Question: If Brahman as per Advaitha was Nirguna, how can it assume forms and create everything ? How can something which is formless take forms and create all materials in universe ?
Comment: Formless Brahman doesn't create Universe. The Maya which resides in formless Brahman creates Universe.
Comment: There is no universe .
Comment: @ParabrahmanJyoti haha great answer, but the question is asked from Vyavaharika plane of existence.
Answer: This question assumes that Nirguna Brahman and Saguna Brahman or Isvara are different. They are same.

Who is Ishvara? Janmadyasyayatah - "From whom is the birth,
continuation, and dissolution of the universe," - He is Ishvara - "the
Eternal, the Pure, the Ever-Free, the Almighty, the All-Knowing, the
All-Merciful, the Teacher of all teachers"; and above all, Sa
Ishvarahanirvachaniya-premasvarupah - "He the Lord is, of His own
nature, inexpressible Love." These certainly are the definitions of a
Personal God. Are there then two Gods - the "Not this, not this," the
Sat-chit-ananda, the Existence-knowledge-Bliss of the philosopher, and
this God of love of the Bhakta? No it is the same Sat-chit-ananda who
is also the God of Love, the impersonal and personal in one. It has
always to be understood that the Personal God worshipped by the Bhakta
is not separate or different from Brahman. All is Brahman, the One
without a second; only the Brahman, as unity or absolute, is too much
of an abstraction to be loved and worshipped; so the Bhakta chooses
the relative aspect of Brahman, that is Ishvara, the Supreme Ruler. To
use a simile:Brahman is as the clay or substance out of which an
infinite variety of articles are fashioned. As clay, they are all one;
but form or manifestation differentiates them. Before everyone of them
was made, they all existed potentially in the clay, and, of course,
they are identical substantially; but when formed, and so long as the
form remains, they are separate and different; the clay-mouse can
never become a clay-elephant, because, as manifestations, form alone
makes them what they are, though as unformed clay they are all one.
Ishvara is the highest manifestation of the Absolute Reality, or in
other words, the highest possible reading of the Absolute by the human
mind. Creation is eternal and so also is Ishvara........Those who
attain to that state where there is neither knower, nor knowable, nor
knowledge, where there is neither I, nor thou, nor he, where there is
neither subject, nor object, nor relation, "there, who is seen by
whom?" - such persons have gone beyond everything to "where words
cannot go nor mind", gone to where the Shrutis declare as "Not this,
not this"; but for those who cannot, or will not reach this state,
there will inevitably remain the triune vision of the one
undifferentiated Brahman as nature, soul and the interpenetrating
sustainer of both - Ishvara. ..... Bhakti, then, can be directed
towards Brahman, only in His personal aspect. "The way is more
difficult for those whose mind is attached to the absolute!" Bhakti
has to float on smoothly with the current of our nature. True it is
that we cannot have any idea of the Brahman which is not
anthropomorphic, but is it not equally true of everything we know? The
greatest psychologist the world has ever known, Bhagavan Kapila,
demonstrated ages ago that human consciousness is one of the elements
in the make-up of all the objects of our perception and conception,
internal as well as external. Beginning with our bodies and going up
to Ishvara, we may see that every object of our perception is this
consciousness plus something else, whatever that may be; and this
unavoidable mixture is what we ordinarily think of as reality. Indeed
it is, and ever will be, all of the reality that is possible for human
mind to know. Therefore, to say that Ishvara is unreal, because He is
anthropomorphic is sheer nonsense. It sounds very much like the
occidental squabble on idealism and realism, which fearful-looking
quarrel has for its foundation a mere play on the word "real". The
idea of Ishvara covers all the ground ever denoted and connoted by the
word real, and Ishvara is as real as anything else in the universe;
and after all, the word real means nothing more than what has now been
pointed out. Such is our philosophical conception of Ishvara.

The Complete Works of Swami Vivekananda III.37-42
It is the Maya Sakti of Brahman who creates the universe. Brahman, when sakti is active, is called Ishvara or Saguna Brahman. Brahman is called Nirguna Brahman when Sakti is inactive. A man is called father when he has a child and is not called a father when he is childless.
A better analogy than given above would be the sun. The difference between the Nirguna Brahman and Saguna Brahman is that between the noon Sun and the evening Sun. The noon Sun is enormously bright and yellow while the evening Sun is less bright and red. In spite of this difference in appearance it is the same Sun that is being absorbed.
Why do Bhaktas say that Brahman is a Person and Jnanis say that Brahman is Impersonal? The answer is that Bhakti marga makes it possible for a Bhakta see Brahman in the realm of Sakti and hence Brahman appears as a Person. The method of Jnana marga takes a spiritual aspirant outside the domain of active Sakti and hence Brahman appears to be Impersonal. It is the same Brahman which appears to be different due to the two different methods.
Comment: Thankyou sir ! Wonderful quotation
Comment: But Pradip the Brahman and Ishwara are the same in the same way Brahman and Jiva are same, but Jiva cannot create the Universe. Infact Brahma Sutras clearly say even after liberation creation and sustenance of Universe belongs to Ishwara and not Jeevis. So all this is happening in Vyavaharika plane, and Brahman being akarta can't interact with Vyavaharika plane
Comment: Isn't saying, Formless Brahman doesn't create Universe. The Maya which resides in formless Brahman creates Universe, more appropriate?
Comment: I have added another analogy that will hopefully make it clearer than before.


Will my kitten have medium or long hair?

Question: I just adopted this cutie. She is five or six weeks old. I am pretty sure she will not be short haired from the ear tufts, but I'm curious how long you think her hair will be? I have had medium haired cats but never a long haired cat and don't know how to tell the difference when they're kittens. Mainly I want to know how much brushing I should expect to be doing, lol.
Answer: Your cat will be medium length hair.
You should get yourself a good brush and start to brush your cat on a weekly basis. This is mostly so your cat gets used to be brushed, as you will need to brush out knots in your cats fur from time to time.
Regular brushing is a good way to avoid hairballs before they become a problem.
This is the type of brush I use on my cat. She is shorthaired.
All cats will at some point in their life need to be brushed, long haired cats need to be brushed weekly and old cats need to be brushed as a result of reduced mobility.
Comment: How can you tell she'll be medium length hair vs. long? I'll buy a brush like that :)


Should you mention your sources of inspiration somewhere?

Question: Should you mention your sources of inspiration somewhere? Let's say you borrow a lot from Greek mythology, Shakespeare, and take some world-building ideas from some famous author. Should you mention them in your book somewhere. How is this usually done? I am assuming some famous authors are open and fully transparent about this.
Answer: As you have added the tag "copyright" to your question, let me first clarify that inspirations are irrelevant to copyright, there is no legal obligation in any form in this case.
The usual way is to have an acknowledgment section at the end of your book where you can thank everyone involved in the project and where you could include a list of people who have inspired you.
Answer: David Drake often includes an "Author's Notes" section in his novels.
These are placed before the text of the novel.  You can skip them, and I suspect many people do.
If you read them, though, you will find some insights into how current events and ancient history combined to produce the story.  There are often times anecdotes about how characters, things, or places got their names or descriptions.
I enjoy the "Author's Notes" as much as I enjoy the stories.

It is a rare story that doesn't share some plot elements with older works.  Sometimes it is purely coincidental, sometimes it is deliberate.
Any "road story" is going to have elements of Homer's Odyssey in it.  Even if you've never read it, just writing an interesting "road story" will involve things that happened to Odysseus.  There will be things that hinder the trip, and things that tempt your hero to give up the quest, etc.
In the same way, pretty much any new story will bear some similarity to earlier stories.
It is also fairly common to write a story that uses characters from mythology - complete with their names and attributes.
Some of the most realistic stories come from authors who know history and mythology, and who can meld them with their own ideas to carry their own messages.
Authors like Drake give you a window into the thoughts that go into making something fresh and modern out of ancient history.
Answer: Easter Egg hunt:
I will shamelessly admit I take inspiration from all sorts of global mythologies. But I'm not inserting a shoutout to Homer in my books. Instead, I place references, names and allusions to the things I take inspirations from into my book. For those who are fans of mythology (or who like to Google everything) My work is filled with Easter eggs.
So I wrote a novel inspired in part by several Greek gods and characters who interacted with them. After my initial draft, I realized my book shared significant similarities to the Oresteia, a cycle of Greek plays that function a bit like the backstory to the Trojan war. Rather than trying to make the book less like the Oresteia, I decided to enhance this. As I edited, I added small additional references, or accentuated the things that were already similar. So now Artemis, Nemesis and the Furies are central names in the work, and if you read it, you can clearly see Clytemnestra reflected in the mothers of the story. While I didn't change the parts of the story that DIDN'T follow the Oresteia, even here there are subtle tie-ins to Helen of Troy (Clytemnestra's twin sister).
Anyone who finds a name in my book can Google it, and will probably find some kind of tie-in to where the character or story line came from. So a clever reader would know that if there are three brothers of the Heydrich family, and the two surviving brothers are named Eugen and Tristan, they could tell me the name of the remaining brother even though it never appears in the story.
So reward your diligent and curious readers with pretiola (Google it, it's the origin of the word pretzel). Someone who doesn't care won't pay that much attention, and those who do will feel like they're in on a secret.


When the base year changes, does it affect data at current prices as well?

Question: I'm trying to collect current GDP data for India from 1990-2016. But, India changed its base year in 2011. So, to get a continuous series, do I have to change the data to a common base?
Comment: Possible duplicate of [Why do we change the base year?](https://economics.stackexchange.com/questions/11656/why-do-we-change-the-base-year)
Comment: For the lazy one (or if you want to have a benchmark to compare your calculation), see [here](http://data.worldbank.org/indicator/NY.GDP.MKTP.CD?locations=IN).
Comment: in some cases that base year is not mentioned in data set or by data provider, how can we find out which year is the base?
Answer: Yes,
If you initially had GDP data at some base year $Year\;x$ for some $Year\;y$
$$I_{\frac{Year\;y}{Year\;x}} = \frac{GDP_{Year\;y}}{GDP_{Year\;x}} \times 100$$
If your base year has now changed to some base year $Year\;a$ for some $Year\;b$
, $a > x$, then you should convert the GDP data from year $b$ onwards to reflect the initial base year, $x$.

$$I_{\frac{Year\;b}{Year\;x}} = I_{\frac{Year\;b}{Year\;a}} \times I_{\frac{Year\;a}{Year\;x}} $$
Further proof,
$$\frac{GDP_{Year\;b}}{GDP_{Year\;x}} = \frac{GDP_{Year\;b}}{GDP_{Year\;a}} \times \frac{GDP_{Year\;a}}{GDP_{Year\;x}} $$
This way you will be able to get a continuous and consistent series based on some base year, $x$. If there were multiple base years, the data would be meaningless since it would reflect on changes with regard to different periods of time - ie, you would not be able to draw a definite conclusion.
An index compares the value of the current year against the value in the base year.
In this case, you might be looking for the current GDP value for every year from your data-set. As an example, if $$I_{\frac{2001}{2000}} = 110, \; and \; GDP_{2000} = 200, \; then \; GDP_{2001} =220.$$

When comparing data with changing base years, for eg,
$$I_{\frac{2001}{2000}} = 110, \;I_{\frac{2002}{2001}} = 105,$$
You can see that this does not mean the GDP in 2002 is $10\%+5\%$ higher than 2000. Instead, the actual GDP =
$$I_{\frac{2002}{2000}} \times GDP_{2000} = I_{\frac{2002}{2001}}\times I_{\frac{2001}{2000}} \times GDP_{2000} = 115.5 \times GDP_{2000} = 231$$
or you can break this down to
$$GDP_{2000} = 200$$ $$GDP_{2001} = GDP_{2000} \times I_{\frac{2001}{2000}} = 220$$ $$GDP_{2002} = GDP_{2001} \times I_{\frac{2002}{2001}} = 231 $$
 Thus this is why you have to change your indexes to reflect on the same base year, since your calculated values of actual prices will differ.
Comment: Thanks Joshua. Just a quick question. Isn't current data supposed to be based on current prices? That's what got me confused. Why is current data affected by base year changes?
Comment: @ChiragYadav, I have edited my answer to include an example. Hopefully this will help. The index is the ratio of current prices of the current year, against the prices in the base year. Thus when the base year changes, the base year price changes too. Therefore indexes with different base years cannot be compared with each other, since a 10%(Index 110) growth from 2000 to 2001 and a 5%(Index 105) growth from 2001 to 2002, does not equal a 10+5% growth in 2000 to 2002, as shown in my example. Your continuous series can be charted by taking the indexes of 90'-16' against 90', or the actual GDPs.
Comment: Also, here's a question similar to yours that i just found : [How to handle change in base year of index?](https://economics.stackexchange.com/questions/15953/how-to-handle-change-in-base-year-of-index)


Dollar bars in Advances in Financial Machine Learning book

Question: Does anyone have use the dollar bars for building a strategy? I would like to know what ways you guys might be interested to set the dollar bars' parameter ( the dollar value ). I have thought of one way is to take the EMA of the past 20 days' daily dollar value but that seems not robust enough.
Answer: If you read the literature in the references and bibliography sections you will see that a common technique is to sample about 50 times a day. This is done by calculating the 30 day moving average of volume and then dividing by 50.
This will give you the threshold level needed for sampling on a volume clock.
Comment: Thank you very much Mr Joubert.


Present Simple or Present Continuous?

Question: Can we use the Present Simple in this sentence : As you know, I try to learn Chinese. Or is it better to use the Present Continuous?
Comment: What **are you trying** to say, exactly?  The two tenses mean different things.
Comment: The simple present is used for things that you do on a consistent, regular basis (*"I **brush** my teeth every morning"*), or for things that are common or natural (*"The sun **rises** in the east"*).  The present continuous is for ongoing actions.  Note I ask what you **are trying** to ask, because that is what you are *currently* doing.
Comment: Could you explain what  this sentence means with the Present Simple?
Answer: With the verb try, the simple present I try does not refer to something you are doing now, at this time in your life. Rather, it refers to an effort you  always give.
You mean "now", and so for that meaning you would say I am trying to learn English and chess.

You have decorated the place very nicely for the party!
  -- I try.

There, I try means,  "I am always willing to put in a good effort. It is in my nature to try to do a good job."

Present Simple or Present Continuous?


Renault Clio 5 motor oil

Question: Which type of motor oil is suitable for Renault Clio 5 sce 65 with petrol engine?
I think a 5w30 but i don't know what type.
Maintenance and warranty sheet : norm RN 17 , engine oil volume 3.40 L , degrees of use according to the outside temperature -15c -20c -25c 5w30 and -30c 0w40 , manufacturer recommends castrol oil.
Comment: Do you have the Owners Manual?  This information should be there.  I searched for an online copy but didn't find it but it will be available from Renault.
Comment: i have it but only recommends castrol oil for engine no specification
Comment: Welcome to Motor Vehicle Maintenance & Repair :o)
Comment: There is nothing special about Castrol.  Castrol oil is going to meet the same API specs as any other oil you might buy for gasoline powered automotive use.
Answer: The current spec is API-SN or SN+, either of which meets or exceeds all the requirements for your Renault.  You can purchase Castrol if you like and I've found that often that brand is reasonably priced.  Sometimes other brands are on sale.
Comment: I'm from europe , do you know ACEA specification. The engine doesn't have turbine and particle filter.
Comment: Same answer, Castrol is a mass market oil not some specialty type.  Check out a bottle of it in your market and see what specs are listed.  Then see if there is another brand with the same specs available at a better price.
Comment: API SN+ is developed for turbocharged engines and i found for clio 5 sce65 a genuine renault rn 17 castrol 5w30.
Answer: A complete answer for clio 5 sce 65 engine oil must be on the label : norm RN 17 , ACEA C3 , API SN .
Norm RN 17 : Compatible for all engine gasoline (except RS and ALPINE) and for new diesel engines Euro 6 from June 2018 and Diesel not equipped with FAP. Backward compatibility on RN 0700 and RN0710 standards.

Renault Clio 5 motor oil