How to find order of convergence in finite element method computationally when exact solution is unknown for time dependent problem

Question: Say for heat equation or Burgers equation with nonlinear boundary condition. Exact solution is unknown.
So I am taking for small mesh size the discrete solution as exact solution. Then how to write the coding part for $L^2$ and $H^1$ error in Matlab?
Comment: Welcome to SciComp.SE. If your question is about how to code something, this might be the wrong place to ask. If not, then I think that you can rephrase your question.
Answer: If the exact solution is unknown, then yes you have to take the smaller grid as reference. Then you run your simulation with different mesh size, each one varying by a factor 2 and you compute the norm $L^2$ as :
$$
\vert \vert u-u_{ref}\vert \vert_{L^2} = \sum_{i=1}^n \sqrt{(u(i)-u_{ref}(i))^2}
$$
with $n$ the number of grid nodes for the considered mesh. Finally, you plot this quantity in respect to the factor size in a log-log plot and the slope of the curve will give you the order. I can suggest you to look at this NASA website : http://www.grc.nasa.gov/WWW/wind/valid/tutorial/spatconv.html
Don't remember for $H^1$.
An applied mathematician tolds me once that the order of convergence for a specific method is dependent on the choice of the norm, it may be more relevant for a specific case to compute the order with the $L^{\infty}$ norm or the $L^1$ norm or whatever norm you decide to define. If anyone has an expertise here, it would be great to have a detailed explanation.
EDIT : see also https://www.kth.se/social/upload/52ea4f1ff2765454c236fe79/ConvRate.pdf


Resources for the Goethe-Zertifikat A1

Question: Are there any coursebooks for the Goethe-Zertifikat A1?
I have found some material on their website, but that seems quite limited. thanks
Comment: @HubertSchölnast A1 is the lowest level in CEFR, The Großes Deutsches Sprachdiplom corresponds to C2 in the CEFR, i.e. the highest level. That's a huge difference with regard to the learning materials you need. Definitely *not* a duplicate.
Comment: Related: http://german.stackexchange.com/questions/4488/what-do-i-need-to-know-to-pass-the-a1-or-a2-exams-from-goethe-institut
Answer: I am using a book called Vorsprung.  https://www.amazon.com/Vorsprung-Communicative-Introduction-Language-Culture/dp/1133937608
It covers lots of material, starting from total beginner to B1 or B2.
Also good online exercises (that complement Vorsprung but are helpful regardless of whatever course/book you chose): http://www.nthuleen.com/teach.html

Resources for the Goethe-Zertifikat A1


The Ethics of Finding Comfort in Religion: Balancing Personal Benefits and Societal Harm

Question: Is it morally justifiable for individuals to continue practicing a religion solely for the psychological comfort it provides, while turning a blind eye to the potential dangers of the religion's power dynamics and its potential to oppress others? How can one balance personal beliefs and benefits with the societal harm caused by religious institutions?
Comment: @DavidGudeman Some Christians practice their religion in a liberating way, some do not. The distinction between opprossive and liberating is not one between religions but between ways of practicing any religion.
Comment: Some religions are oppressive; others are liberating. And even the liberating religions like Christianity can be called oppressive by people who don't want anyone to be liberated.
Comment: "*Is it morally justifiable for individuals to continue practicing a religion solely for the psychological comfort it provides*"  People abuse drugs and alcohol for the "psychological comfort it provides" I think your question has merit but your wording is harsh.
Comment: There's a reasonable case to be made that we all behave according to the 'psychological comfort' our actions provide us.
Answer: Research has linked 'religiousity' to a number of personal benefits, eg reduced depression Is there a relationship between spirituality/religiosity and resilience, reduced risk of heart-disease and cancer (!) Association of Religious Service Attendance With Mortality Among Women, and to resist or recover from addiction Religious Faith and Spirituality May Help People Recover from Substance Abuse + many more papers. There's also research suggesting the impacts of loneliness are comparable to obesity, & religious participation can help with the former. And religiosity even correlates with a longer lifespan, by an average of about 4 years.
There are clear social risks though. Extremism, like Puritans or the Wahabi Islamic sect. Religious conflicts, like the three centuries of the European Religious Wars, or Sunni-Shia conflicts like embodied in the Saudi-Iran conflicts, or the ethno-religious Tamil-Buddhist Sri Lankan conflict. Resistence to social change, like the biblical prohibition against usury which by ceasing to be enforced in Christendom probably significantly helped to end Feudalism, or gender decrees that reduce opportunities for skilled workers and bright minds to define themselves, or scriptural passages were used to justify slavery in Christianity and Islam.
So, I'd say your question holds clear merit. There are well evidenced personal benefits. And much discussed social negatives. We can of course find converse cases, religiosity has been linked to unwillingness to seek mental health support, and Abolitionists were were primarily motivated by religious ideas as were the first vegetarians who wanted to reduce animal suffering. But I'd say the balance is clear.
Religions in order to persist, must tend towards being conservative, and resistent to change, and that seems to relate to a lot of the problems they generate. I think it's very interesting to look at the precise mechanisms for reform, in different religions - this seems an often neglected topic. In Islam, the Koran is the revealed word but distinct schools of jurisprudence have arisen, with associated sects, it makes secular governance difficult to achieve in Islam because Mohammed was explicitly a political as well as military leader and gave political decrees for his times. Christianity has been crucially shaped by it's Ecumenical Councils, the East West split ended Hesychasm, and the rise of Protestantism led to doctrinal fragmentation that has allowed for instance Prosperity Gospel churches to gain large followings while having been declared formally heretical by most other Christian groups. In Judaism they have the Beth Din Rabbinical courts, and the tradition of the Talmud continued there is of detailed exegesis by argumentation, this has proved remarkably capable of both updating and keeping the spirit of religious decrees, like how interpretation of Eruv has maintained Jewish areas, ethno-religious nationalism is creating big issues in Israel but then it also did since at least Roman times - the Nevuah or time of prophets is considered to have ended, they could alter the 'core code'. In Buddhism the Sangha makes decisions about monastic life and exegesis, in Therevada the canonical texts are all considered to be from the time of the Buddha, while Mahayana allows further teachings to be canonical which has allowed it more doctrinal flexibility, but also war-priests and non-celibate monks in Japan. In Sikhism, they allowed 10 gurus over two and a half centuries, then ended that phase with a codified text considered to be the 'final guru', in many ways they picked good bits from monotheism and polytheism, and have a remarkable and interesting practice that includes one of the best charity practices of any major religion, and their ideas should be better known. Hinduism is more culture than religion, with a sprawling array of gurus and mela gatherings where they come to the fore, which has seen hugely dynamic 'religious entrepreneurialism', but also the wiping out of Buddhism in the mainland despite a Buddhist king being first to unify India, and a current surge in ethno-nationalism, Hindu thought has tended to react to react to new faiths then integrate the reaction eg Shankaracharya to Buddhist thought.
When choosing an established major faith, but disagreeing with it on some major point, the degree it is capable of changing must I'd say be an issue. Major religions all have modern sects, branches or interpretations that have arisen to address conflicts or meet culturally varying needs, so it's generally possible to pick and choose tenets, though this may limit how many adherents there are locally, and so the social benefits of practicing. Human institutions are intrinsically problematic, especially when shielded from criticism or accountability. So I'd say there has to be a balance struck, between continuity and capacity to change - we cannot live in the past, without killing the future.
The more interesting idea to me, is can we gain the benefits religions have provided, without the negatives? I really like the idea that religions can be considered as assemblances of 'metis', of practical crafts, of how to live well together: Whence Comes Nihilism The Uncanniest of all Guests?'. Durkheim was arguably the first thinker to really successfully grapple with how religion has been done differently outside of the Abrahamic faith's sphere, and his points about anomie vs social cohesion from enactment of shared attitudes towards sacred values, can help us understand that habeus corpus (no detention without trial), or values of scientists that bind together their international community, can be related to  the mechanisms of religion. There's a lot of overlap I think with Nietzsche, who can be understood better in my opinion by recognising how there is a tension in religious discourse between what we keep and what can be changed, that he wanted a recapitulation of the epoch of (largely) preliterate religious fluidity.
Sapolsky has a great lecture on the possible Biological Underpinnings of Religiousity. The TLDR is, maybe mild schizophrenia has related to hearing intuitions about social needs as commandments, and OCD could relate to rituals that have helped bind together groups doing them. China under communism undertook one of the most thorough purges of organised religion, and yet now is among the most superstitious countries in the world, with big focuses on the power of certain numbers, and 'energy directing' practices that used to exist in pretty much all cultures but have elsewhere largely been consigned to history.
I would make the case Ancient Rome and China by being extremely militarily unified, were able to be very religiously cosmopolitan and diverse. Whereas, the fragmented Holy Roman Empire, or warring Islamic empires with major ethnic divides, tended to use limits on 'religious entrepreneurialism', ie dissent about interpreting religion, to try and limit political fragmentation. So, I would point first of all to the idea securing peace, can help foster space for religious dynamism.
We accrue cultural 'metis' given relatively stable times, and the dynamism of the last century seems to have obscured this. We have major social problems, like suicide being the leading cause of death for ages 16-45, loneliness being a huge problem, and a 'meaning crisis' characterised in various ways. People will innovate ideas towards dealing with these, and in time they will form a cultural body, and future people may call that a religion. But at root there is just an art of how to live better together, and we should all try to learn it, and contribute to that new, and ever-dynamic 'book'.
Namaste.
Answer: Reduce the statement to neutral language and evaluate it, then evaluate the inexplicit premises to see if the evaluation of the neutral language statement is relevant to the specific topic.
Is it moral to participate in an activity which causes net harm to others but provides net benefit to the participants, supposing that one believes that about the activity?
Are some religions such an activity, relative to whatever things would be like without them? What do I know and why do I think I know it?
Are there alternatives, what do they seem to have been historically and in the present day, and are they any better?
If so, do any / many religious people actually believe that their religion causes net harm to others relative to the alternative?
If so, is the net marginal harm per additional religious practitioner positive or negative?
If so, which religions, why, where, and to what extent?
Comment: *"Is it moral to participate in an activity which causes net harm to others but provides net benefit to the participants"* That doesn't seem to be the issue raised, as social harms can simultaneously act as risks (eg of religious wars) while an individual gains benefits. Your *"net marginal harm per additional religious practitioner"* seems out of character with what convinces people to adhere or not to religions. If we were all so logical, it seems unlikely religion would be a topic..
Answer: Certainly one ought not to "turn a blind eye" to injustices committed by institutions  in society--whether he belongs to them or independent of them.  It is fair to say that--based on the universal Moral Code--it would be morally wrong to knowingly support them, just because he derives some psychological benefit(s).
However, one must be careful to not commit the Fallacy of Logic (Over-generalization) by assuming that all religious institutions are prone to (or guilty of) committing social harm. Nor believe that there are not those within erring institutions who are assiduously seeking reformation. The "personal benefits" do not relieve anyone from maintaining vigilance against harmful conduct within any institution, religious or not.
Further, it should be cautioned that, while there may be several psychological benefits for being religious, there are other more important reasons for membership. Most parishioners would find solace in theological benefits for their belonging.
Answer: Of course it's not morally justifiable to avoid moral problems through religion.  There was a commandment to give back on a regular basis in Abrahamic religions and there is good, sound, verified purpose to this.
This is not at all an excuse to escape culpability in one's acts.  Unfortunately, religions such as christianity have normalized the idea of "no fault" in ethical decisions if you follow Jesus ("All of your sins will be forgiven.").  It is completely reprehensible and an act of heresy.
People who use religions to find comfort are avoiding their world.
Comment: There is nothing wrong in finding "comfort" when coming into the Presence of God, where there is not only solace, but instruction in social justice (righteousness), and most importantly, redemption from misconduct (sins).  The error comes when religion is simply used as a crutch alone, or social club, or cultural fashion.  Christianity as taught by Jesus, in no way, condones a "no fault" escapism.  Salvation is not cheap! It cost Jesus His life on a cruel cross, after being incarcerated unjustly by "us."  Social injustice is not normalized in Judeo-Christian theology, (Read Micah).
Comment: @raygrant:  You are screwing around with words.  You just said "salvation is not cheap" and waved away the problem of **personal choice** (*the* issue at hand) by comparing to something completely unrelated:  the crucifixion.  It is unrelated because their choice didn't create that history.  Whatever you want to believe about the historical act *itself* is *itself* an escape -- if you *choose* to believe that it grants you salvation from your own choices, for without choice, you are NOTHING.


batch UPDATE autoload value in wp_options table

Question: After running the following query SELECT option_name, option_value FROM wp_options WHERE autoload = 'yes'; I've found I got 1587 autoloading options values, mostly belonging to custom fields values; since they start with category or _category I am looking for a way to SELECT and UPDATE the autoload value for all at once. I guess an SQL query would be the fasted method but I am not sure about the correct syntax.
Answer: Not a hard task at the end. I've managed to do it in two chunks with
UPDATE wp_options SET autoload = 'no' WHERE option_name LIKE 'category%'; and
UPDATE wp_options SET autoload = 'no' WHERE option_name LIKE '_category%';
Comment: Hi i wonder is there any benefit on this?
Comment: @MichaelRogers Yes sure, if you have plenty of autoloaded options which increase SQL data transfers - it might have a positive effect.


External website in iframe

Question: We currently have requirement to show external website in iframe. External website users will have user name and password and salesforce user name and password as well.As part of the authentication i am sending loggedin user salesforce session id in the iframe url parameter. Now the question using this session id can the external system grant access to 3rd party website by doing callback to salesforce and get the user information? Kindly help..
Comment: Have you read about [Connected Apps](https://developer.salesforce.com/page/Connected_Apps)? Seems like what you're looking for.
Comment: Could you please give more information on the solution? How can i use Connected App to solve above requirement?
Answer: Answering to the question:-

Now the question using this session id can the external system grant
  access to 3rd party website by doing callback to salesforce and get
  the user information?

Yes, if external site can read the session Id and has the url of the instance then it can call the Salesforce and perform tasks based on user.
Problem:
Using Iframe witin Salesforce page comes under Cross-Origin policy violation. It means you can not access a website url within Salesforce which has different domain, protocol and port. So, this solution may not work.
I recommend to use Connected Apps.
Update as per comment:-
You will need to configure external website to match the Username and Org Id registered in external site database. If information received from session ID matched with website database process the automatic logic
Other recommended way:-
Set up the IDP (Identity provider) and single sign-on. This is the most common way to authenticate two systems and verify their credibility. Go through these links and try t0 understand the single this process. You may find several post how we can leverage this feature.
Comment: Hi @Ashwani, My question was little different, using salesforce session id can the external website grant login access to their site?
Comment: I tried your recommended approach to have SSO between Salesforce and external website. But i need to give IDP initiated URL in the iframe. This is giving me Cross-Origin policy violation error. Do you know any other solution for above problem?

External website in iframe


What does the letter in these ATC data blocks indicate?

Question:
Why do some have an F and others have a D?
Comment: What is the source of the image? What else can you tell us about it (what airspace does it show, etc.)?
Comment: @TypeIA It is Sarasota airspace. It is from this Vasaviation video.   https://youtu.be/Wsf6zzmzH8c
Answer: Those letters indicate the wake turbulence category of the aircraft.
Based on context—LFA, callsign "BUCKY," is a flight school and is unlikely to by flying "Upper Large" aircraft—the categorization being used in the video is probably the "Wake Turbulence Recategorization" (RECAT) rules, which is an older version of of the wake recategorization project (see FAA JO 7110.659C, the latest version of RECAT in use before its cancellation). The current standard is known as "Consolidated Wake Turbulence" (CWT) and procedures are defined in FAA JO 7110.126. The wake turbulence category of a particular aircraft type can be found in FAA JO 7360.1. If you had taken the screenshot at a slightly different time the datablock would have shown the aircraft type in the righthand side instead of the groundspeed.
Note also that this is NOT a depiction of a real-world FAA system; VASAviation feeds ADS-B data into their own simulator software. It looks pretty close but you cannot assume it is the same thing that the controllers were seeing at the time.
Comment: Yes, and I said that in my answer... "F" indicates RECAT category F and "D" indicates RECAT category D...
Comment: Do you know what the F and the D by the speed indicate?
Comment: Oh sorry, didn't catch that.


Buffer Overflow EDI but not EIP

Question: Is possible to exploit a program if you can only overwrite ESI or EDI register without EIP?
Program in question does seg fault and overwrite EDI, ESI and ECX but can't get it to overflow EIP. Anyone know why?
Thanks, Tom
Comment: Maybe.  It depends entirely on what the program does with the ESI and EDI (and for that matter ECX) registers.
Comment: It would really help to have a lot more context on this question. What's the program, what's the exploitation method you tried?
Comment: Getting from segfault to exploitation is not always a given and entirely depends on your program. Without at the very least code excerpt from the vulnerable part, it's not possible to answer this question.
Answer: Almost certainly, but it may not translate to a reliable exploit. As you are controlling ESI, EDI and ECX you are most likely controlling a byte copy operation and I'm assuming the crash is caused because you're trying to read/write to an address like 0x41414141.
At worst you can hard code some addresses where ESI points at the start of your shell code, EDI points to the next instruction address (EIP+opcode bytes). ECX should be the length of your shellcode. This will overwrite the next series of instructions with your shell code.
For a more reliable exploit you would have to do some more analysis on how you ended up controlling these registers and what code paths are available depending on what you point these registers at.
Comment: Of course, "This will overwrite the next series of instructions with your shell code." assumes a system without `W^X`
Comment: My guess is if you can set ECX to a smaller (but large enough) value, EDI to a writable page (perhaps somewhere below the saved EIP) and ESI to somewhere within your buffer, you'll end up getting %pc control. As wireghoul implied, EDI, ESI and ECX are commonly used to copy a count of ECX bytes from memory at ESI to memory at EDI. However, it's also used for *comparisons* of memory, so you may be hosed- as an example, both strncmp/memcmp and memcpy/strncpy have this calling convention

Buffer Overflow EDI but not EIP


Whose Brahmin is this? I'm not cleaning up after it

Question: Three things happened at once last night: Raiders attacked Sanctuary Hills, the population went to 11, and a Brahmin showed up. The Brahmin does not count as my 11th settler, there is an actual settler for that, but where did this Brahmin come from? Is it a consequence of having more than 10 settlers?
Comment: I'm not sure what causes it, but I have Brahmin wandering around most of my settlements.
Comment: Add a feeding trough to keep the brahmin, if your dislike of brahmins fades over time
Comment: Should've gone with *"Whose Brahmin is it anyway?"* :P
Answer: The Brahmin come with settlers. They use them to carry their things from wherever they came from to your settlement. If you set up a supply line, they will walk around with Brahmin a lot, as a symbol that the supplies on the Brahmin are carrying things back and forth.
No this isn't because you have more than 10 people.
And no clean up is required, they don't poop.
Edit: If it's a Brahmin that isn't carrying anything, then it's a wild one. You can find them out in the world sometimes in a pack. Sometimes they can wander into your settlement if it's too open or if another animal chased it that way.
The wild ones don't poop either.
Comment: No, not a caravan Brahmin. This is just a regular, totally naked Brahmin that just hangs out.
Comment: Ah, I know where it came from then. I will edit my answer for you.
Comment: Isn't there an item called a brahmin trough or something? I would imagine its a way to get brahmin around to use as food supplies
Comment: @RobertWertz That is correct. There are ways of bringing in Brahmin, for various reasons, if you wanted to. But that isn't the case for this question.
Comment: I also had a random one show up and hangs around my town. I do not have local leader or even 6 cha. It stays pretty consistently in my area though, even through fast travels. So I'm not sure it is a wild one.
Answer: The Nukapedia page on Brahmin indicates that they will sometimes be recruited by your recruitment beacon instead of a settler:

When actively recruiting for a settlement with a recruitment radio beacon, there is a chance to receive a brahmin instead of a settler.

That seems consistent with my in-game experience, in that Brahmin usually show up in settlements that have a few people, which are settlements where I've set up beacons. But, if someone has a Brahmin in a settlement that never had a beacon, it would act as a counterexample.
It also indicates that the Brahmin produce fertilizer in your workshop, and that they increase food production:

Brahmin will increase settlement food production while also producing fertilizer, a component for chemistry that will be placed in the workbench.

I've seen no in-game evidence that that's true. I'm willing to believe that they produce fertilizer, but I'm highly skeptical of the food production claim. I've always been able to account for 100% of my food production via crops, with no extra mystery component that could be attributed to the Brahmin. Perhaps they accelerate the collection of the actual crops, or the rate at which they regenerate after being harvested.
So, they're your Brahmin, and your settlers will clean up after them.
Comment: and you can force them to stand around a particular spot by building a Brahmin feeding trough (it's a derelict bathtub but is actually named as a feeding trough). I believe it's under the 'Misc' section of 'Decorations'
Answer: Occasional it seems a new settler will come with a Brahmin included. I have them on several settlements, some more than others. Did not figure out yet if you can move that same settler around and the Brahmin will follow. In that case you could move all your Brahmins to a single settlement and have your production of fertilizer (they do that) in one place. And you can make drugs from fertilizer and get rich! Or high....


how to deal if input feature are all categorical but target feature is discrete numerical, it is giving exact numerical for known data

Question:
the following data is to detect malnutrition among children under age 5 and the value_r is the percentage estimate of wasting among the population. should I apply the decision tree as an entirely categorical feature input as well target variable?
Answer: you can apply any Machine Learning model on this. This will be regression problem.

if number of classes to particular column are not to many then try to do "one-hot encoding" eg: get_dummy in sklearn.
if there are too many classes for any column try to regroup some of similar to single class.
then apply any Machine learning/ Deep learning model to solve regression problem
Answer: To answer your question:

If your input features are all categorical and your target feature is discrete numerical, you can use a variety of machine learning algorithms that can handle this type of data. Following are the few things that you look into:

Data Preprocessing: Convert your categorical features into numerical values. This can be done through various encoding techniques like One-Hot Encoding, Label Encoding, Ordinal Encoding, etc.

Feature Scaling: Although this step is not necessary for all algorithms, it can be beneficial for some, like K-Nearest Neighbors (KNN) or Support Vector Machines (SVM).

Model Selection: Choose a machine learning model that can handle discrete numerical output. Some options include Decision Trees, Random Forests, Gradient Boosting, etc. These models can handle both categorical inputs and discrete numerical outputs.

Model Training: Train your selected model on your preprocessed data.

Model Evaluation: Evaluate your model using appropriate metrics. Since your target feature is discrete numerical, you can use metrics like Mean Absolute Error (MAE), Mean Squared Error (MSE), or Root Mean Squared Error (RMSE).

Prediction: Use your trained model to make predictions on new data.

If your model is giving exact numerical values for known data, it might be overfitting. This means that the noise or random fluctuations in the training data is picked up and learned as concepts by the model. You can try to reduce overfitting by increasing the size of your training data, reducing the complexity of your model or using techniques like cross-validation, regularization, or early stopping.
Hope I answered your question.


free way to stream to ipod touch without jailbreaking

Question: Is there a free way to wirelessly stream content to an iPod Touch (if it helps, 4th gen with latest 4.3.5 installed) without jailbreaking? If not, will iOS 5 enable me to do this?
Comment: Can you clarify a bit more please. Do you want to be able to stream music from your iPod touch wirelessly?
Comment: I want to stream music /from/ iTunes on my Macbook /to/ an iPod Touch.
Comment: Would Home Sharing enable me to do what I want (it's OK if the iPod streams from iTunes instead of iTunes streaming to the iPod).
Answer: There are a lot of options for this. The easiest ones use a native iPhone application that will cost you a small amount (usually around $2.99 on the app store). But you asked for a free solution so I'll start with that:
Free Option
Jackson Chung over at Makeuseof.com has written a detailed explanation of how to stream your iTunes music library to your iPhone/iPod/iPad for free. It wont be the greatest experience so I'm going to include a couple of the paid options below as well.
Paid Options
These two options use a iOS application to enable the streaming:
StreamToMe — $2.99 on the App Store

Use StreamToMe on your iPhone, iPod Touch or iPad to play video,
music and photo files streamed over WiFi or 3G from your Mac or
Windows PC. No prior conversion or syncing required (huge number of
formats supported without conversion) just tap the file and it plays.

AirPhones — $2.99 on the App Store

AirPhones sends the audio from your computer to your iPhone or iPad
with virtually No Latency. Perfect for wireless, synched audio.

Finally, this option does not require an application installed on your machine as it runs a small server that is accessible via an iOS-friendly web interface on your device.
Remote Buddy — €19.99 on their website

The most powerful remote control solution for the Mac®. Control more
than 100 applications, virtual keyboard and mouse, presentations,
media center software and important system settings right from your
iPhone™, iPod® Touch, your Apple® Remote or one of the many other
remote controls supported by Remote Buddy!
Comment: I've used StreamToMe and can confirm that it works nicely and does what you want.
Comment: I hadn't thought of this. Absent an AirPlay solution that I can use from iTunes, this will work. Thanks!
Comment: @zpletan I'm afraid a solution similar to the ones above will be the closest you get without jailbreaking. Apple has marked the APIs required to achieve what you want "private". This means only Apple can use them AND get into the App Store. If you're interested in Jailbreaking there are a few more options.
Comment: That makes sense. Still, I want to make sure. (And no, I'm not interested in jailbreaking.) If nothing else happens in the bounty period, I'll award it here. Thanks.
Answer: Isn't this exactly what Home Sharing does? On your iPod, go to Settings > Music and enter your Apple ID and password under Home Sharing. Launch iTunes on your Mac or PC (and enable Home Sharing there too). Back on your iPod, go to Music and tap the More button, and you'll see an entry for Home Sharing. Tap that and you can play any of the music stored on your Mac/PC on your iPod.
Comment: I couldn't figure out how to get the iPod to see my library. This did the trick. Thanks!


what is the difference between a class and a library?

Question: I googled, and was informed that a library is made up of multiple relevant classes. But in Codeigniter, I found that there is virtually only one Class in every Library. Sorry for my limited knowledge for this, but I would appreciate it if you could enlighten me a little bit on this. Thank you very much!
Comment: i library, may have nothing to do with classes, it could just be a collection of procedural functions. a class has a well defined definition, a library, at least in php does not.
Answer: The difference is a semantic one.
A Class is an implementation of a specific piece of functionality (usually completely encapsulating the functionality.
A Library is a collection of units of functionality (or just one) that add functionality. Notice I tried to stay away from the word class in that definition.  Libraries can be procedural, functional or OOP.  That doesn't detract from the fact that it's a library.  Classes just help the abstraction when dealing with OOP.
A Framework is a library that imparts architecture choices on how you write code.
Every framework is therefore a library.  Not every library is a framework.  CodeIgniter itself can be used as a framework or a library.  The difference is if you let the libraries direct your architecture, you're using a framework.  If you do not use the architecture bit, it's a library.
It's definitely a pedantic difference, but a significant one.  As a gross-over-simplification, if you're doing a formal architecture and understand why everything is layered out how it is for your application specifically, you're using it as a library.  If instead you're building it that way because that's how CI does it, that's using a framework.  Both have significant benfits, but it's worth understanding the difference.
Answer: In general programming terms, not every library has to be made of multiple classes. In fact, not all libraries have to be made up of classes either — it really depends on the implementation (and sometimes the language). As Wikipedia starts off (italics mine):

In computer science, a library is a collection of resources used to develop software. These may include subroutines, classes, values or type specifications.

CodeIgniter has its own definition of "library", in this case it simply calls each third-party application class its own library. Despite that, you can include other classes in the same library file, as long as you have at least one class with the same name as the library file.
Answer: Checking the CodeIgniter docs:

When we use the term "Libraries" we are normally referring to the classes that are located in the libraries directory and described in the Class Reference of this user guide. In this case, however, we will instead describe how you can create your own libraries within your application/libraries directory in order to maintain separation between your local resources and the global framework resources.

I don't think of a "library" as specific to a fixed number of classes or files. Does this quote refer to the specific usage that has you confused?


Can you use Firebase.Auth in Xamarin.Forms?

Question: I am exploring app development and doing Xamarin.Forms, and I want to use Firebase, so far looking at the Authentication thing. The problem is that I am not sure if possible and how to use it in Xamarin Forms, I've found some native documentation and something about forms but I couldn't really understand it or it was updated.
Answer: Check the Nuget package of xamarin:
Android:
https://www.nuget.org/packages/Xamarin.Firebase.Auth/
IOS:
https://www.nuget.org/packages/Xamarin.Firebase.iOS.Auth/
Here is a tutorial for Xamarin-forms:
https://evgenyzborovsky.com/2018/03/26/firebase-authentication-in-xamarin-forms/


Bond whose amortization scheme initiates at a later time in its life?

Question: Is there any type of bond whose amortization initiates at a later time in its life? For example the first year we observe interest-only payments and after year 1 there initiates an amortization schedule.
Answer: Indeed there are. But they do not have a particular name.
They are mostly based on contracts specific to the counter-parties. Amortization can start in a prespecified, say, coupon payment date later than the first initial coupon payments. This also applies to drawdowns of the notional. Fully-drawn, partly-drawn etc.
I hope this helps.


Why can't I read/sync my Mobi format ebooks on the kindle app for mac?

Question: I have uploaded several ebooks (Mobi format, not bought via Amazon) onto my Kindle personal library, and I can read them without a hitch on my Kindle device, but not on the Kindle app for Mac. Is this a restriction placed by Amazon or a configuration problem? Is there a workaround? All I want is to synchronyze all of my ebook reading on Kindle, Mac and Ipad.
Answer: You certainly cannot synchronize them with Amazon software, because they allow onto their cloud only their products.
You can do it however with a very nice application, Calibre, which exists for Mac as well as for Linux and Windows.
If you want, you can get around the DRM (Digital Rights management) restrictions by means of a smart app, which you can download here. This will allow you to synchronize all your e-books across different reading platforms, by using your Mac as the synchronizing agent.
Comment: Thank you for your answer, but I have been using Caliber, and that is not really the issue. The problem is that, while my entire ebook library (Amazon-bought or not) is available on the Kindle device, the CALIBER-CONVERTED EBOOKS (.mobi) are NOT READABLE OR SYNCHRONIZABLE on the KINDLE FOR MAC app. All the ebooks I converted on Caliber and uploaded to the Amazon library are DRM-free, by the way.
Comment: @Joe Thanks for point out what I have missed. Just for the sake of curiosity: can you read all books with Calibre? If so, why do you need the Amazon app for Mac?
Comment: Because I don't want to do all of my ebook reading exclusively on the Mac, but would prefer to synchronize my reading progress on Kindle, Ipad and Mac. It's a really nice Kindle feature that I would like to have for my entire library, if I can: that way I can stop reading on one device and pick up at the same point on a different device later.
Comment: @Joe Though I never use this feature, it does make sense. However, Amazon cloud simply does not allow me to upload, and thus synchronize stuff which I did not directly buy from them, not even pdf files.


Are Apple Human Interface Guidelines questions off-topic on SO?

Question: I've seen questions like this one that have no coding implications per se, but revolve around Apple's HIG and as such can only be answered by developers. Are these off topic or not? Why?
Comment: Don't we have a UI.SE?
Comment: Yes, we do, but that doesn't address HIG per se either. If HIG questions *should* be there, perhaps all HIG questions (9 or 10 tagged ones) should be automigrated to UI.SE.
Answer: I consider questions that ask about whether the specific use of a control would violate the Human Interface Guidelines to be on topic for Stack Overflow.  These tend to be different from your normal questions that ask about ways of improving the user experience, because there are definitive rules that guide their usage, and there's normally a specific solution to the issue that requires code.
The Human Interface Guidelines also shape my answers to questions.  If someone asks how to do something in code that will violate the guidelines (like changing the color of alert views), I'm more likely to answer by telling them not to do that rather than just blindly giving them code that I know will cause trouble for them later on.
More subjective questions on user experience might be good candidates for the User Interface Stack Exchange site, but I think these specific HIG-related ones that affect your application design belong here.
Comment: good answer. btw, how *do* you change the color of alert views?
Comment: @Moshe - If you're masochistic enough to try, I used Quartz to redraw the entire look of an alert view in this sample application for my class: http://www.sunsetlakesoftware.com/sites/default/files/QuartzExamples.zip (I couldn't resist the challenge by someone from the class).  With a little Core Animation to make it pop on the screen, you could change the background color used for that drawing and have your own ugly alert view.  There's no way it would make it past the reviewers, thankfully.
Comment: Are you sure it won't get past reviewers? My game is inherently B&W and this would be the finishing touch. I could show my own custom alert, why is this any different? I just want to make it grayscale.
Comment: @Moshe - The language "The background appearance of an alert is system-defined and cannot be changed." and "You can't customize the width or the background appearance of the alert view itself" in the HIG is pretty explicit.  However, you might be able to create an alert that is just different enough from the system-provided controls (different border, size, etc.) that they would identify it as purely custom UI and you wouldn't fall afoul of this restriction.  Games that have their own completely custom UI don't need to follow the HIG to the letter.
Comment: @BradLarson - My app is a game (http://itunes.com/apps/nippon). It uses UIKit but is supposed to be B&W.
Comment: @Moshe - However, you're still using the standard iOS interface elements, so you're restricted to using those in the way that Apple allows (in the interest of platform consistency).  As I said, if you came up with something that was clearly distinguishable from a normal alert in design they probably would not complain.  In the screenshot for your application, the alert you're providing would be more appropriate as a sheet anyway, which can be made black and white.  Alerts should be rare within your application, and should indicate errors or exceptions, not prompts for more info.
Comment: @BradLarson OK, are action sheets also modal, like alerts?
Comment: @Moshe - Yes, and they're intended to be used as prompts for more information, which is exactly what you have here.
Answer: Have you checked our User Interface Stack Exchange site??
Seems like a perfect fit if you ask me!
Comment: So then the HIG questions are off topic then. Okey dokey.
Comment: Well I'm not a user there, but Interface Guidelines smells like UI to me
Comment: In general, the HIG might be a better fit for UI.SE, but this question seems specifically about the App Store approval process, which has traditionally been a legitimate topic on Stack Overflow.


How to set volume control using a mouse shortcut?

Question: I used to be able to use btnx in ubuntu 11.10 to do this, but now i can't find the software from the software centre. can anyone help me with this?
Answer: If you want to install btnx, you can use these .deb files:

32 bit: main program / gui
64 bit: main program / gui

EDIT: Convenience.
Comment: Thanks, but after downloading the deb file and running it, it says dependency is not satisfiable: btnx-config (>=0.4.9)
Comment: maybe i should use source or sth like that to install, but i dont really know how to do this. perhaps it is time for me to learn doing so.
Comment: i am sorry, i just saw the gui link, will try doing it now
Comment: Awesome! Be sure to mark my answer as the solution, so that people know this issue is solved. Glad I could help.
Answer: Did not work for me. Better follow these instructions:
How to set volume control using a mouse shortcut?
if needed: sudo apt-get install indicator-applet-complete
then: Ctrl-Windows-right_click on top panel -> Add to Panel... -> Indicator Applet Complete
Answer: If you want to change the volume with the wheel of the mouse when you are in the corners of the screen, I can suggest you this :
Volumouse for Linux


Is there a WebDAV log for SharePoint 2013 Farm?

Question: Our developers are experiencing intermittent timeouts when transferring files to a SharePoint 2013 Farm. Is there a WebDAV log?
Comment: Hello @tjreeddoc welcome to SharePoint SE , please don't forget to **Mark**  the correct and useful answer as accepted in case it helped and solved your issue, Thank you for your contribution. For more details check https://sharepoint.stackexchange.com/tour
Answer: There's no specific WebDAV logs, however:

WebDAV is nothing else than specific HTTP requests: WebDAV requests do appear in the standard IIS logs.
WebDAV requests are processed by SharePoint: any application error should appear in the SharePoint ULS logs.

If you need to watch more deeply what happens at the protocol level, you'd need to inspect the network traces with a tool like HTTP Fiddler (client side) or WireShark (client/server side).


Can I work in EU with my student visa?

Question: Can a non-EU citizen holding a Romanian student visa (Masters Degree), find a job in Germany and move there before finishing his study?
Comment: Romania is not part of the Schengen area. You need a visa for Germany. Job interviews can be done on a short stay 'C' visa (unless your citizenship allows visa-free visits), actually starting to work needs a long stay 'D' visa.
Comment: @o.m. Your comment would be true even if Romania *were* part of the Schengen area.
Comment: @phoog, as a student in Schengen he could travel to Germany e.g. for a job interview, but not to work.
Comment: @o.m. true enough.  When I said "your comment" I should instead have limited it to the statements concerning actually starting to work.
Answer: Not on the basis of the student visa.  Work authorization for citizens of countries that are neither in the EU nor in the Schengen area is handled by national law.  The only country that can issue a document permitting the student to work in Germany is Germany.
Furthermore, since (as noted in a comment) Romania is not part of the Schengen area, the Romanian student visa does not even allow the student to travel to Germany, much less work there.
Whether the student must wait for the end of the studies to apply for a German visa is up to Germany.  If the student already has the qualifications for a German work visa without finishing the studies in Romania, it should be possible to apply for a German work visa, which, if granted, would allow the student to move to Germany before the end of the studies in Romania.
Answer: Yes, but it depends on how many hours is the job and what is the job related to...
I was a student too and i was able to have a side job (neben Job in German)
here some info:

Rules for students
Students from the European Union, Iceland, Liechtenstein, Norway and Switzerland enjoy unrestricted access to the German labour market and have practically the same rights as German students. However, if they work more than 20 hours per week they must pay certain insurance contributions (just like German students). For students from other countries, special legal regulations apply:

International students from other countries are allowed to work 120 full days or 240 half days per year. They are not allowed to be self-employed or work as freelancers.
Students who want to work more need permission from the Agentur für Arbeit (Federal Employment Agency) and the Ausländerbehörde (foreigners' office). Whether they are given permission depends on the situation on the labour market: the chances are better in regions with low unemployment.

An exception is working as an academic assistant. There is no limit to how many days academic assistants may work. They still have to inform the foreigners' office however. If you are uncertain what category a job falls into, you should seek advice from student services or the International Office.
Comment: What is the source of the quoted information?  Regardless, it probably does not apply, because (I suspect) "international students from other countries" refers to such students who are studying in Germany with a valid German student visa.  That is not the case here.
Comment: https://www.daad.de/deutschland/in-deutschland/arbeit/de/9148-der-nebenjob/
Comment: I don't see any evidence that this applies to someone who is studying in -- and has a student visa issued by -- a different EU country.

Can I work in EU with my student visa?


Do collusive agreements always lower output?

Question: I read that collusion between firms in a oligopoly setting make sure that consumers experience higher prices and lower output because the firms start to function as if they are in a monopoly. Is this always the case? Is it possible that output instead increases?
Answer: You would have to define the word collude precisely. An example of legal collusion/cooperation where output increases:
In some swimming pools, cinemas, etc. the buffet is run by a different company. Everything else being the same, most people prefer to go to a pool/cinema with a buffet rather than to pool/cinema without one. Thus the buffet contracting to be present is potentially increasing the sales of the other establishment.

In the textbook case of Cournot-oligopoly firms colluding in the market of a normal good where there are no externalities the statement is true.
It is difficult to say "always", as one can usually come up with somewhat special/convoluted scenarios where the outcome is flipped.
E.g., there is a concept called minimum resale price, where the supplier would prohibit the retail store from selling its product under a price X. There are a lot of theoretical models where this is shown to result in higher prices and hence, a loss to the consumer; as a result the practice is prohibited in many places (e.g., EU countries). However, in the past decade models have also shown that such agreements could potentially improve the quality of service to such a degree that the consumer would actually benefit, even if the prices are higher.
So a lot depends on the exact nature of your models. In models with asymmetric information even beliefs about beliefs can play a large role, frustrating forecasters, as these are nigh-on-impossible to measure accurately.
Answer: "Is it possible that output instead increases?". It's possible if some outside agent will reward them for increasing their output. Like maybe USA could convince OPEC to increase their output, in exchange for some kind of political favors, in order to lower profits of Russia from selling oil. I don't say that it's very feasible, but scenario like this seems to be in the realm of possible.


angularjs infinite scroll in a container

Question: I'm trying to use angularjs infinite scroll
It seems to work only if the scroll is relative to the browser window.
I would like to do infinite scroll in an inner DIV, i.e. I have a page with a generic wrapper and an inner div for displaying the actual content.
The wrapper page is set to elapse the entire window, thus it is never scrollable.
but the inner div that contain content, has its own scroll bar.
How to I get the infinite scroll to work relative to the inner content div scrollbar?
Answer: In case anyone searches the same and comes here - here are usefull links:
https://github.com/BinaryMuse/ngInfiniteScroll/pull/7 (pull request and discussion)
https://github.com/hlsolutions/ngInfiniteScroll/tree/scroll-on-any-lement (fork with neccessary functionality)
https://raw.github.com/hlsolutions/ngInfiniteScroll/scroll-on-any-lement/src/infinite-scroll.coffee (source itself)
You can use it this way (example is in haml):
.div-with-overflow
  %ul{data: {'infinite-scroll' => "getItems()", 'infinite-scroll-disabled' => 'cannotGetItems()', 'infinite-scroll-parent' => 'true'}}

Providing an 'infinite-scroll-parent' => 'true' will make parent element to be used for calculations instead of a window.
Comment: I have a similar issue where I want to specify the container for the scroll but it does not work. Shared the link for the demo. Can anyone tell me what the issue is? https://stackblitz.com/edit/ngx-infinite-scroll-ngdxwc?file=src%2Fapp%2Fapp.component.html
Answer: Here is an example in plain HTML:

Two gotchas here:

For infinite-scroll-distance to work properly, the child element of your infinite-scroll directive has to be the elements you are enumerating, so the scroll distance trigger will fire correctly.
The value of infinite-scroll-container in this example is double-quoted class name .content then wrapped by single quotes. If you read the source, the string value eventually gets fed into document.querySelector. You can read the documentation on that to see what value it expects.

You can also use the infinite-scroll-parenthelper like @trushkevich suggested if the immediate parent element of your infinite-scroll directive is the scrollable container.
Comment: I've noticed that the addPage() (or w/e anyone calls it) gets called a lot. The directive seems very sensitive. Is there a way to make it less sensitive and call addPage() less frequently? I've tried infinite-scroll-distance at 0 and 2000, but it's calling the function well before I scroll to the bottom in either case.
Comment: Nice catch on the quotes. Fyi, for me it was infinite-scroll-container="'.container'"
Comment: Can you please help me with this http://stackoverflow.com/questions/33190595/using-infinite-scroll-in-angularjs-and-jade
Answer: This thread is a bit old, non-the-less still relevant.
As it seems, ng-infinite-scroll merged in some of the forked solutions, and now supports the following (undocumented) attributes:
infiniteScrollContainer lets you set the container by passing in a query selector or function or html element
infiniteScrollParent simply tells it to use the parent as the container (instead of $window)
Sample use:

Comment: http://stackoverflow.com/questions/33190595/using-infinite-scroll-in-angularjs-and-jade
Comment: Thanks, this worked for me. I change `infinite-scroll-container` with `infinite-scroll-parent="true"`
Answer: I'm suggesting another infinity scroll: ui-scroll it has the most fundamental feature "destroying elements as they become invisible and recreating them if they become visible again." - avoids creating watcher and make you app sluggish
Comment: It should be mentioned that uiScroll works like a charm when applied to a container as well.
Answer: Open the ng-infinite-scroll.js file and change all reference of $window to $("#my-content-container").
Remark: a robust solution would be to add an attr parameter to the infinite-scroll with the id of the container.
Answer: use this code there is no plugin
in controller do the following
$(".Scrollx").scroll(function () {
        if ($('.Scrollx').scrollTop() + $(this).innerHeight() >= $(this)[0].scrollHeight) {
            $scope.limit = $scope.limit + 5;
        }
});

Set the limit variable as you want to display first-time
example: $scope.limit=5
Comment: This one is a lot better than ng-infinite-scroll


Will my ranking drop if I don't comply with GDPR?

Question: I have a site that is not doing well on search and I don't know why. My site doesn't have the GDPR popup, will that be an issue with Google rankings? If so, how does Google know?
Comment: I'd like to use this opportunity to point out that forcing the user to click on an OK button on a cookie banner has nothing to do with GDPR compliance. According to the GDPR, you either have a good, legitimate reason for processing the user's data (in which case no consent is required), or you don't (in which case a *freely given* and *informed* consent is required - which is a criterion that many banners don't satisfy and which Google cannot "check" automatically).
Comment: I don't believe that Google are looking for GDPR compliance per-se, but (at least according to my SEO expert and his group) care that you have a privacy policy.
Answer: To my knowledge, Google has never announced that GDPR compliance is a factor in their ranking algorithm, so it's reasonably safe to assume that your ranking issues stem from a different cause.
However, GDPR compliance can come into play if you integrate Google products into your website, for example AdSense.
For a general overview of ways to increase ranking, see:
What are the best ways to improve a site's position in Google?


Not able to query RoleInTerritory2 field from UserTerritory2Association in Apex class

Question: I want to query the RoleInTerritory2 field from UserTerritory2Association  sObject. I am logged in as System Admin profile but still not able to query this field. Starnge thing here is that I am able to query this via developer console. Does anyone have any idea reagrding it?
It gives me an error :
No such column 'RoleInTerritory2' on entity 'UserTerritory2Association'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names.
Answer: Got the problem. There was an API version conflict. It works for API versions 30 above.
Comment: The class where I was trying to use UserTerritory2Association object, was of API version 30 which doesn't support it. I changed the API version for the class that solved my issue.
Comment: Would you mind specifying which API version you changed it to? I tried this and it didn't solve my problem.


What is the function of the payload_checksum field in the Bitcoin protocol

Question: According to the protocol specification at the Bitcoin wiki, each message header includes the  first 4 bytes of sha256(sha256(payload) as a packet checksum. I suppose this checksum is used for packet validation, but I do not see any benefit of this, as Bitcoin utilizes TCP which already has (as far as I know) full protection from lost and damaged  packets. So... why this checksum? Is it to maintain compatibility for future UDP clients?
Answer: "Full protection" is a relative term.  TCP packets include only a simple checksum, effectively just the sum of all the 16-bit words in the packet.  See RFC 793 section 3.1.  This is a fairly weak integrity protection mechanism.  The Bitcoin designers may have felt the use of sha256 gave better protection.  It may also, as you say, have been intended to provide forward compatibility for running Bitcoin over UDP or other protocols.  It may even just have been paranoia.
Comment: Bitcoin originally didn't have this checksum, but Satoshi was having a lot of trouble with various garbled packets on the network, so he added it. It's better than the TCP checksum, and it also covers cases where bad data is sent to the socket. See the post [here](https://bitcointalk.org/index.php?topic=56272.msg669898#msg669898) starting with "I'll take a look a the logs."
Comment: But this weak protection is good enough for other sensitive protocols like FTP and HTTP? They don't include checksums, right? (HTTPS/SFTP does of course, but just plain FTP/HTTP errors could be disastrous too). Thanks for answering though :)
Comment: @jori It's not necessarily good enough, but it's what we've got.
Comment: I'm going to research the TCP checksum capabilities a bit further and then post back as I cannot believe the designers deliberately choose a bad schema for such an important task. It would be disastrous if using some executable file send across the network using FTP, resulted in unexpected.behavior.
Comment: @jori: Bear in mind that the design is almost 40 years old, and it was important that the checksum be easy to compute on primitive hardware. CRCs were probably considered but rejected as too expensive, and our modern cryptographic hashes had not been invented.
Comment: @theymos: Thanks for the history.  Since this feature doesn't affect the block chain, it could easily be added without risking a fork.


What kind of tree is the giant tree in Downton Abbey?

Question: In the opening sequences of Downton Abbey series 1 and 2 there is a massive tree near the house. When it appears in the show characters are often shown sitting on a bench underneath it. What kind of tree is it?
Comment: Never seen the show but does this tree provide some plot significance or is it just a piece of scenery?
Comment: It's just scenery, but a couple of key conversations take place under it :)
Answer: It is a Lebanon Cedar.   From the wikipedia page about Highclere Castle - the location for the fictional Downton Abbey.

The famous 18th century seed collector Bishop Stephen Pococke was a
  friend and brought Lebanon Cedar seeds from a trip to Lebanon
Comment: Thanks. This tree blows my mind every time I see it. For me it is a symbol of the grandeur of the house and family.
Comment: I knew it had to be a non-native tree. No English tree classification guides could identify it as a native tree.
Comment: Yeah, quite a few British stately homes and castles have non-native plants and trees as the owners in the 19th and early 20th century liked collecting stuff like that - before the issue of 'invasive species' became more of an issue.


Can professors hire assistants from their own salary?

Question: Usually teaching assistants or research assistants will be hired by money from the department or grants, but can they be hired by a direct pay from a professor's salary?
Comment: When my husband was a PhD student, his supervisor paid him cash to teach some tutorials. This was not legitimate, as he was paid less than the official rate, but it seems it happens.
Comment: I mean of course they can, the issue is what relationship these assistants can bear to the university.
Answer: Probably not, though professorial funding can get tricky. In the US, most departments or colleges handle the funding of TAs directly. They are normal employees and are (more and more) entitled to benefits. If a prof just took money literally out of their own pocket and paid a TA, this would circumvent tax withholding, the purchase of insurance benefits, etc. TAs need to be employees of the university. At the same time, since they interact with students and appear in the classroom, TAs need to have official status with the university. Since direct payment by a professor would bypass this, I doubt very seriously that it would be allowed.
However, once a professor has a grant, money becomes more flexible. It's entirely possible for a professor to be paid 9 months by the university and end up funding more than 3 summer months through grants. NSF has its 2 month rule to try to prevent this, but through multiple agencies, a lot is possible. Agencies allow Principle Investigators the flexibility to move salary money between personnel within a grant almost at will, so it could be that a prof could take one of those months of their own salary from the grant, and spread it across several (at half time) for a student. This is pretty common. It wouldn't be direct, the student would be paid by the university and have official GRA status, but it would, sort of, come out of the prof's pocket, depending on your point of view.
Comment: I'd also add that some profs I know make plenty on their 9-month salary that even though they have summer months funded on grants, they never pay themselves and use that money (quite generously, IMO) to fund students and research staff.


Some kind of short circuit or bad connection maybe

Question: I have a 00 grand am.  Every time I start my car my time is on 12 but my stations are still set.  What could this be?
Comment: Is this an aftermarket radio, or the factory original?  Has it ever worked since you've had the car?
Comment: Yes factory radio and yes it has always worked.
Answer: There are two separate power circuits that go to the radio.  One is always on and keeps the clock going and any other temporary settings.  Your preset stations are stored in permanent memory so the battery can be disconnected for vehicle service without you having to reset them all.  The other power circuit comes on when you turn the car key to power the rest of the radio and speakers.
These two circuits will be protected by two different fuses.  If you trust the pictures on this website, the fuse you want to check is in the passenger side fuse box.  The one labeled FUSE BATT should be the one that provides constant battery power to the radio.  Sorry, but I can't speak to the accuracy of those particular diagrams.
That said, a fuse is not the only place a circuit can fail.  The radio could be internally damaged, and the wire for that battery connection could be broken somewhere.  Checking the fuse is the easiest thing to do.


Automate OS installation and associated packages

Question: We are having a small software firm and we are using ubuntu for our employees. Whenever a new machine bring to our office, we do install ubuntu, and many required packages such as LAMP,skype,IDEs,filezilla etc and integrate the machine to our AD using likewise etc. So every time we do it manually and we need an effective way to do this. I need something automated or create an iso from the existing one (fully installed machine) that can be used for the installation afterwards.
Comment: I reinstall a lot of different versions, but just created a bash script to automate just about everything. But if hardware is identical you may be able to use something like Clonezilla? http://clonezilla.org/
Answer: Use Ubuntu Customization Kit (UCK) to create your own customized Live CD/DVD/USB.  Then you can use that CD, DVD, or USB to install your own customized Ubuntu onto other machines.
sudo apt-get install syslinux-utils libfribidi-bin uck

(I've also included a couple of important required packages in the above command).
Here is the UCK Launchpad Page: https://launchpad.net/uck
After you install the uck package, there are a two bugs you should apply fixes for:
https://bugs.launchpad.net/uck/+bug/1245981
https://bugs.launchpad.net/uck/+bug/1435019
After installation, launch the UCK GUI from the Unity Dash.  Select your language preferences, and then select the "Run Console Application" option, so you can install your required software (LAMP, Skype, IDEs, filezilla etc.) using apt-get and make necessary configurations.
(Note that the final compressed iso may not be greater than 4GB, but you should have plenty of space to install all the software you need).
Answer: If you want something straightforward you must use remastersys , although it is discontinued there is a way to install it on ubuntu 14.04 . Two steps and you just wait until your iso is ready to burn.
http://www.diolinux.com.br/2014/04/remastersys-no-ubuntu-1404LTS.html
This step by step  is in portuguese but i can help if you need . After install just type in terminal to create a distro including all your programs and updates:
sudo remastersys dist

Or to include your home folder and configs
sudo remastersys backup


Replacing oil pan

Question: When replacing an oil pan, I will have to remove a motor mount and jack the pan up a few inches, followed by wedging sm block by harmonic balancer. To keep it up. I have never done anything like this. Can someone tell me anything specific I do or don't need to do when doing this? Is there a chance I could mess my oil pump or sensor up?
Comment: Welcome to Motor Vehicle Maintenance & Repair! What engine are you working on? If you let us know this, we can more easily tell you do's and don'ts
Answer: You can raise and support the engine without using a jack by using this kind of engine support bar, which you can make yourself from lumber. You could also buy or borrow one of them.
If you put the car on ramps first, then set up the bar, disconnect the engine mount and lift the engine, you can do the whole job without a jack or jack stands, no wedges and without worries of damaging something due to jacking it.
Depending on the vehicle, the engine mount bolts might be for one-time-use, so be sure to check the published procedure and obtain new, never-installed engine mount bolts if needed. (That type is torqued into the plastic range upon installation, and if ever used again, they will eventually come loose. You'll know you have those if the procedure says something like "torque to XX ft-lb plus 1/4 turn".)
As Paulster2 said, tell us the year / make / model / engine for additional tips.

Replacing oil pan


computing AIC or BIC for nonlinear regression models

Question: Is it possible to calculate AIC or BIC for nonlinear regression models like SVM, regression trees, artificial neural network, and others. AIC and BIC can be estimated from linear models, but I have not seen AIC and BIC being computed for these nonlinear regression models. So, wondering if anyone can provide their opinion with some examples? Thanks.
Answer: The AIC and BIC are both functions of the likelihood.  Any model that is fit by maximum likelihood has a straightforward AIC and/or BIC.  Some models that are fit with a penalized likelihood can also provide AIC.  For example, a generalized additive model provides AIC by counting effective degrees of freedom rather than parameters, and the maximum of the penalized likelihood.  I suppose this could be done with ridge regression as well.
One way to think of a regression tree is as a linear regression on dummy variables that indicate which partition the data falls into.  If you recast your tree that way, then there is nothing stopping you from fitting it with least squares and then computing AIC the normal way.
But why would you do this when packages like rpart automatically cross-validate for you?  Cross-validation is almost always better than AIC for model selection.  Other models could probably be shoehorned into a framework that makes AIC computation feasible.  But the question will generally be: why?
Comment: @Abijah I guess what I was saying was that if you were to run an experiment on many datasets, you'd find that a model selected by (well-designed) cross-validation would show better test set performance than a model selected by AIC.  AIC penalizes complexity through a heuristic:  it's just the number of features.  Sometimes, however, the number of features is not the best proxy for complexity.  Rather than proxying for complexity, CV directly tests whether a given model configuration will overfit.  Complexity is now always bad.
Comment: Do you know of some work that indeed compared cross-validation with AIC or other information criterions and demonstrated the superior performance of cross-validation with AIC for non-parametric regression models? I ran and compared the regression models using 10 fold cross-validations with five repetitions using CARET packages, and I used R2 and RSME to pick the best models. But an anonymous reviewer asked me to use information criterions to evaluate the effectiveness of models. So, wondering if someone can help me craft an appropriate answer to that question. Your response helps. Thanks.
Comment: Sounds like the reviewer needs to be "handled".  The best way to mollify this person probably depends on the precise sort of model you used.
Comment: I agree, and the only way to do this is to cite some existing works if there are out any without doing any additional computations. Further, I am not a statisticians, and sometimes answering this type of question to stat savvy becomes very tricky.
Comment: You can cite either "Elements of Statistical Learning" or "An Introduction to Statistical Learning" (both free online), but, flipping through, the authors make clear that CV is generally better, though they never explicitly state that they are superior to AIC.  I suppose that general statements like that are generalizations, and thus always wrong.
Comment: "Cross-validation is almost always better than AIC for model selection" i am used to both being useful for different things. what do you mean by this?
Comment: that makes a lot of sense


The observer effect, how is related to death of human brain or consciousness?

Question: Are we just a measurement device that interacts with quantum wave function/photons or something more? if not then can we die/be destroyed as observer?
Comment: Why would you think that QM singles out yourself as "special"? Any reasonably classical measuring device like particle detector is also an observer. Can a detector be destroyed? Of course it can.
Comment: The wave function collapses upon interaction, but not upon observation. The existence of the actual observer is irrelevant. For example, a detector near a slit in the double slit experiment interacts with the passing particles. Upon interaction, the detector can give you an output to inform you of the interaction. Well, if you cut the output cable from the detector, the detector would continue interacting with the passing particles, but you would have no idea if it did or not. The result of the experiment would be the same (in lines of interference) whether anyone conscious observes it or not.
Answer: I think its safe to say that the vast majority of people in the QM field generally ignore this question (what is an observer/observation) as nonsense in the first degree. We may not understand wavefunction collapse (assuming it exists) but that doesn't mean you have to invent nonsense to explain it. You may not know exactly how your car works either, but you can still drive it, you don't have to imagine unicorn horn in the gas tank.
I say this because in my own brain I simply assume that the entire observer issue is not really an issue, and that someday someone will "figure it out". And when they do, all questions of this sort will simply disappear. It will become like "how fast does a dirigible need to fly?" the day after the 747 entered service.
Comment: You're getting downvotes for the simple fact that you even bothered to answer this question. Some questions are best left unanswered.
Comment: Why not? We invent nonsense every day: dark energy, origin of species, social justice...


What criteria should be considered when selecting a residential real-estate appraiser in the US?

Question: As a buyer, if a private appraisal should be performed on residential real-estate prior to purchase, what criteria should be considered when selecting the appraiser, and how can someone locate and evaluate the required information about competing appraisers efficiently?
Comment: I think this is quite location-specific. Are you in the US? I know the customs and practices around real estate are quite different between the US and the UK, so if I wrote a (UK-based) answer to your question it probably wouldn't help you. Could you add a country tag, edit the question, or comment to indicate where in the world you are?
Answer: Usually when you buy a home, the mortgage company will send out a third-party neutral, and anonymous appraiser. This is to ensure that the appraisal is fair and objective. But I'm not a real estate expert. However, I would ask them questions like how many appraisals do they do? How long have they done it for? How many properties in the area have they appraised? Do they have the license? Are they well-known? Etc. etc.
Comment: Also note that you can challenge the appraisal if it is a hindrance to your purchase. We bought vacant land once and the appraisal came back at half of the actual market value because the appraiser misread the dimensions of comparable lot. We challenged it and got an updated appraisal that matched our expectations.
Comment: @DStanley I have also challenged an appraisal that [almost prevented our sale](https://money.stackexchange.com/a/72854/10997) because there were some typos in it that impacted the final value.


Is there a ZIP code I can enter when paying-at-the-pump in the USA with a foreign credit card?

Question:
In the USA, many pay-at-the-pump fuel dispensers that accept credit cards require a 5-digit numeric zip code that corresponds to the billing address of the credit card.  In Canada, for instance, we have 6-digit alphanumeric postal codes, so it's not obvious what you're supposed to type in since the gas dispensers have only numeric keypads.  Entering '00000' or '90210' seems to always result in failed authorization.
Is there a zip code that works for credit cards with foreign billing addresses?
Comment: Would you consider broadening the question to 'foreign credit card'? I think that would make it more useful to others.
Comment: @AndrewFerrier - Edited to 'foreign' rather than 'canadian' credit card.
Comment: @AndrewFerrier: I concur, though the Canadian credit card seems to be an exception, AFAIK.
Comment: Some US gas stations are card-only during the night. Both cash and foreign cards are useless in that situation.
Comment: As of late I've not been asked a zip code for my card at fill up.
Comment: Interested to know how this process works with a Japanese credit card (and the 7-digit postcodes this country has. Do you cut the end 2 digits, or the first 2?
Comment: Brazilian credit cards worked fine typing any valid zip code from the US, I've just opened Google Maps picked up any point on the map to copy its zip code. I'm.sure it didn't check anything for my cards, it just asked for a valid local zip code.
Answer: Canadian Credit Cards
Many fuel dispensers in the USA (for sure in Hawaii, apparently elsewhere in the USA as well) accept the numbers-only from the postal code of a Canadian billing address followed by two zeros.
So, if your Canadian billing address is right beside Schwartz's Deli in Montreal where the postal code is  H2W 1L2, you would enter '21200'.  Where the '212' are the numbers from the postal code, and the '00' is padding to get to 5 digits.
Interestingly, if your billing address is in Head-Smashed-In Buffalo Jump, Alberta where the postal code is T0L 0Z0, you actually would enter '00000'.
Edit: I just tested this on January 23rd, 2014.  It still works.
Comment: Interesting.  How did you learn this?
Comment: While Head-Smashed-in-Buffalo Jump is one of the more colourful place names in Canada, the 0s are easy to find. Small rural places that all share the same postal code have them to allow expansion later.
Comment: @EdwardThomson american here. does this mean i may not need to provide my full address when paying with a credit card online—just the numbers? that would be great.
Comment: @NateEldredge: Although I'm American and can't test this, this makes sense.  Software implementing AVS (the mechanism of credit card verification that verifies addresses) is expected to send only the numeric parts of the address and/or zip code.  (Eg, if your billing address is "42 Anystreet Ln", your address is only verified as "42".)
Comment: I wonder whether this scheme works for other countries as well as Edward Thompson's comment would suggest.
Answer: UK Credit Cards
I have a UK credit card and have had mixed results using my card at the pump. Sometimes no ZIP code is asked for and it works fine. Also, sometimes entering 00000 does work (I'm guessing because it's not subsequently using the ZIP code entered). In about 80% of cases, though (and it does seem to vary as to where in the US you are), I've had to go into the gas station - although they generally seem well equipped to handle the exception process (by which I mean, at that point it doesn't seem to matter that it's foreign - I just ask for X$ of gas and they charge it - the difference being refunded if it's unused).
Comment: The trick for Canada has worked for me with a UK credit card, too: use all the digits in your postcode then pad with zeroes. So for example, if your postcode is SW**1**A **2**AA, your "zipcode" would be **12**000.
Comment: In my experiences with using a UK card in the states, 00000 doesn't work, and the staff in the gas station are able to handle the exception, but I wouldn't say "well equipped to handle"...
Comment: The MTA website actually says that for using international cards at Metrocard machines, use the zip code 99999 (very last bullet point here: http://web.mta.info/metrocard/mvms/index.htm) so perhaps that would work in gas pumps too...
Comment: At unsocial hours the gas station may be unmanned, so the only option is to use a card at the pump. As it happens I have a US credit and debit cards, but have yet to memorise the zip code associated with those cards, I therefore have to remember to use the Debit card and its PIN. Have yet to try my UK Debit card.
Comment: Incidentally, I have also found that 00000 works at some other automated machines (such as the Metrocard top-up machines in New York City).
Answer: German Credit Cards
I've had mixed results with German credit cards. Since we also have 5 digits ZIP codes, the match should be fairly easy. However, on some occasions it worked perfectly, while on others it didn't and I had to see the cashier. All in all, there doesn't seem to be any kind of rule or system - at least not to me.
Comment: No, you definitely need to enter your German billing addresses ZIP code. On my first encounters with a US pump I tried my hotel's ZIP code, because I didn't know  that the ZIP code is used to validate the card and not for market research. Only when I started entering my home's ZIP code it worked almost every time.
The success rate also seems to depend on the card itself. In my experience, American Express causes the least amount of trouble in the US. It's almost always accepted, even in vending machines.
Comment: probably different handling agents use different mechanisms. The smart ones notice it's a foreign card and just ignore the number, stupid ones assume all numbers are US numbers and can't match the resulting US zip to the card (doh!), and still others try to do a foreign lookup and fail because non-US credit card agencies don't do such things, again causing a fail.
Comment: On a trip to the US this past summer I used my German credit card at gas stations.  At every single station where I had to enter a ZIP code, I put in my German postal code.  The authorization _always_ failed and I had to go inside.
Comment: @Kyralessa Yes, things seem to have changed in the last several years. Don't know if it's because of the cards or the gas stations themselves but I also experience more and more stations where I have to go inside. But there are still some examples where paying at the pump still work, even with the postal code.
Comment: If I had to guess, I'd say that the pumps are designed not to fail if there's no zip-code checking service, because then _nobody_ could pump gas.  So perhaps in the past a lot of these pumps weren't actually connected to anything that could verify the zip code, and any five digits would suffice.  But by now they've mostly finally got their back ends hooked up, and the zip code checks are real (and, as usual in the US, completely unaware that there are any other countries in the world).
Answer: Swedish Credit Cards
Swedish credit cards work fine. You can type in your Swedish zipcode (also 5 digit) but I honestly doubt the system checks for foreign cards.
Answer: I have UK and Italian credit cards. Italy also has 5 digit postal codes and I've sometimes been able to use the postal code at the pump with an Italian card.
I've also called my credit card company and asked if I could put a temporary address on a credit card so that I could have a zip code associated. In my case they said I would have to have that as my only address but could change it back later. In the end I decided not to do that, but might be worth asking if your credit card company can do it. Perhaps just put the address of the hotel you're staying at.
As other people have said, I've also had luck using just the digits of my UK postal code padded with zeroes. I've never been able to use all zeroes.
The mechanism that the gas station uses, is the credit card Address Verification Service. It's worth noting that there seem to be restrictions on this in various US states as noted in this cpn site:

There are some controversies and legal issues when requesting AVS
  information. For example, in California and Massachusetts it may be
  illegal to ask for ZIP code information, as this is seen as a privacy
  violation.

This may explain why all zeroes are accepted in some places and not others.
AVS works differently with different card suppliers, so it may be possible that a Mastercard works with a foreign 5 digit postal code, or zero-padded postal code, whereas an Amex doesn't, or vice versa.
Answer: Australian credit cards
Australian credit cards don't seem to cause much of a problem here - I was able to use 90210 (which is always my go-to American zip code, probably like many!) on gas stations in both Florida and New York.
This was with an Australian Mastercard.
Comment: This wasn't the case for my Australian MasterCard in California, I had to go in to the server.
Comment: Just used my tassie postcode + trailing 0, worked with visa debit card.
Answer: Swiss credit cards
Not tried yet at the pump.
At a Long Island Railroad ticket machine in New York City, the code was asked. I accidentally tapped the "Continue" button on the touchscreen witout typing any code, and it worked.
FYI The zip codes in Switzerland have 4 digits.


How to change the RAM allocated to an OS in VirtualBox?

Question: I have already booted up an OS but find it too slow to work on. Is there a way to increase the RAM which was allocated to it initially?
Answer: Pretty easy to do.

Power down the VM (the guest has to be off, not just not running but with a saved state).
Discard 'Saved State'
Open the VM's settings.
Open the System tab.
Change the "Base memory" value to however much RAM you want.

Remember, the VM will reserve all the RAM you allocate to it on your host, so make sure you have enough spare RAM.  Most modern OSes will deal with the amount of RAM changing just fine, but you may still run in to trouble, so make a snapshot first.
Comment: Many settings are greyed out and cannot be altered. One must first do "Discard Saved State". This is safe because I shut the VM down previously. After that the RAM can be expanded.
Comment: With VirtualBox 5.2.4 I didn't need to discard the saved state. I just followed the list, except for point 2, and it worked. So maybe they changed it in recent versions.
Comment: Fabio's comment caused me to investigate more.  I was seeing all the VS settings greyed out and would have had to discard saved state to edit them.  So I launched my VM and then in then in the VM's OS I properly shut down the OS.  Once I did that then I could edit the VM's settings, they were no longer greyed out and I didn't need to discard saved state.  So that seems to be the key.  If you closed the VM's window without properly shutting down the OS in the VM the settings will be greyed out. But if you properly shut down the VM's OS, they will be editable.
Answer: In addition to Dennis M, to change Vm machine memory settings via command line, I used :
vboxmanage modifyvm "Centos7_Vanila" --memory 1000

Where "Centos7_Vanila" is my VM name.
To Get your imported / listed VMs run following command :
vboxmanage list vms

Comment: Just a note: the default unit seems to be megabytes and it will **fail** if you try to add the unit like `--memory 1000M`.
Answer: There is a fast way in terminal, I named the virtual machine "Android 8.1 Oreo", so just modify that on the following command:
vboxmanage modifyvm "Android 8.1 Oreo" --vram 256

I had a maximum of 128.
Comment: The question is not about VRAM.


Does the fact that $\lim\limits_{n\to\infty} |f(n)/f(n-1)| = 1$ imply that $\lim\limits_{n\to\infty} f(n)$ exists?

Question: This question was inspired by another question I asked on this site. For that question, I had thought that if the differences in subsequent evaluations of a function, $f(n)$, defined with a domain of only the natural numbers (including $0$) converged to $0$ as $n$ approached infinity, then this would show that $f(n)$ would converge to some value. I was wrong in this assumption. Another idea I had is that if the ratio of one evaluation to the previous converged to $1$, this would also imply existence of a limit. This seems more likely because of the ratio test, but that applies only to terms of an infinite sum and only implies convergence when $|a_n / a_{n-1}| < 1$. Is my assumption true? Can it be proven somehow by the ratio test? If not, what is a counterexample?
Comment: Another counterexample is $f(n)=n$.
Comment: When you say that $\lim\limits_{n\to\infty} f(n)$ exists, do you mean that exists finite?
Answer: Let consider as counterexample $f(n)$ such that

$f(n)=1$ for $n$ even
$f(n)=-1$ for $n$ odd
Answer: As soon as I wrote this question, I believe I found a counterexample for it. Consider the function as partial sums of the harmonic series.
$$f(n) = \sum_{k=1}^n \frac{1}{k}$$
If we consider the limit of the ratio, we get
$$\lim_{n\to\infty} \left|\frac{f(n)}{f(n-1)}\right| = \lim_{n\to\infty} \frac{\sum_{k=1}^n \frac{1}{k}}{\sum_{k=1}^{n-1} \frac{1}{k}} = \lim_{n\to\infty} \frac{\frac{1}{n} + \sum_{k=1}^{n-1} \frac{1}{k}}{\sum_{k=1}^{n-1} \frac{1}{k}}$$
Separating this into two fractions gives us
$$\lim_{n\to\infty} \left(1 + \frac{1}{n\sum_{k=1}^{n-1} \frac{1}{k}}\right)$$
Because the harmonic series diverges, the denominator of the second fraction approaches infinity. Even if we did not know that the series diverged, we know it is greater than zero. That multiplied by $n$ as $n$ approaches infinity would show the denominator to tend to infinity anyway. This leads us to the limit being equal to $1$. Because we already knew that $\lim\limits_{n\to\infty} f(n)$ does not exist, this leads to a contradiction and disproves the original statement.
Comment: Ok it's mainly a matter of convention and notation, I'm used to distinguish between the two cases according to the definition given. Now it is clear to me what you were asking for! Thanks
Comment: @gimusi I was taught in my calculus class that saying a limit tends towards infinity was just a more descriptive statement implying that the limit does not exist. Saying the limit is equal to infinity is just an abbreviated way of saying it tends towards infinity. I believe the first answer on this question: https://math.stackexchange.com/questions/127689/why-does-an-infinite-limit-not-exist offers a good explanation.
Comment: Why do you say that limit does not exist? Usually we say in these cases that $f(n) \to +\infty$. We say that a limit doesn't exist when for example $f(n)$ oscillates between two different values or other cases for which we can't define a limit (finite nor infinite) according to the definition.


Confirming sender identity read function call with MyEtherWallet.com

Question: It does not seem to be the case that MyEtherWallet.com is supporting read function sender restrictions such as onlyOwner modifiers or similar, so basically it is impossible to restrict particular function reads to certain groups/tiers of people. Why is this not an option? I believe it should be possible to confirm similar to write functions by accessing a wallet through one of the many options.
Answer: Modifiers like onlyOwner cannot be enforced on view or pure (or the deprecated constant) functions, since when reading from outside, any view-able data is public. A simple read operation does not involve a transaction, and thus does not have a msg.sender.
I imagine calling a view function with an onlyOwner limitation from another contract might fail, however, but there is no way to prevent it from web3.
Edit: As smarx points out, it is possible to set msg.sender for a view function call, but perhaps not through MyEtherWallet. In any case, this is optional and should not be relied upon for security. Any data on the blockchain should be treated as public and readable by all.
Comment: `eth_call` does take an optional `from` parameter (though I don't think MEW supplies it). When a `from` address is supplied, that is the value of `msg.sender`.
Comment: @smarx Thanks for pointing that out, I've edited the answer
Comment: "As smarx points out, it is possible to set msg.sender for a view function call, but perhaps not through MyEtherWallet." this is what I observed as well. But it doesn't really answer the question regarding why it shouldn't be possible? how is any view-able data public when reading from outside, this is only true if the data is stored in the contract, if it's a calculation then this is false and if the function call reverts on trial then the return data calculation remains private
Comment: @NowsyMe Even if you could enforce that, the raw data itself is still public, and stored on every node's storage. Anyone could go and pick it out of the actual chain state if they wished. Remember, nothing is encrypted in the chain, only signed and verified. The actual data is effectively plaintext
Comment: I see what you mean, thanks for elaborating on the subject


Does Molten Silver Strike or Steady hand allow Whirlpool strike to have higher range?

Question: Molten Silver Strike allows to add Solar Wind boosts to Mithral Current attacks and adds +5ft/4init level to their range. Whirlpool strike allows you to attack every enemy in your weapons reach. Steady Hand (Solar) adds 30 ft range to your attack. Do they work together to allow you to attack everyone in 35+ range?
Answer:
Mithral Current strikes that allow you to attack enemies at range as a melee attack

(Molten Steel Strike description, emphasis mine)
Most Mithral Current strikes do not allow you to attack enemies at range as a melee attack. Whirlpool strike certainly doesn't. The only strikes that this feat are applicable to are iron wave, silver wave, quicksilver wave, and mithral wave.
Steady hand adds 30 feet of range. Range and reach are different—range is only for ranged attacks, reach is only for melee attacks. Whirlpool strike is melee, and so you need bonuses to reach—bonuses to range, as from steady hand, do not improve it.  Molten Steel Strike does not change this, because Molten Steel Strike only applies to the Mithral Current strikes that allow attacking at range. With Molten Steel Strike, you could use steady hand on iron wave so that it can attack out to your close range + 30 feet, but not whirlpool strike.
To improve whirlpool strike, you need options that improve your reach. The most obvious of those is to increase your size, though there are other options.


Is it okay to do a PhD in the domain you barely know?

Question: I consider myself a Software Engineer. However, I recently accepted a PhD position in Data Science domain (i.e. which I barely know). I am slightly motivated because I believe that data can have a tremendous impact for the society. Despite of that, I still have some doubt. How do I cope with the doubt? Is it normal for every PhD student?
Comment: Presumably if you were offered the PhD position it was because you demonstrated sufficient knowledge of Data Science to convince someone you were familiar with the domain?
Comment: [Obligatory link to our still by far top-voted question.](http://academia.stackexchange.com/q/2219/4140)
Comment: @SaberAlex My question was perhaps more rhetorical. If the decision-makers for the PhD program have deemed your knowledge of Data Science sufficient to begin the PhD then perhaps you know enough to begin the PhD. A PhD is a learning experience. You're not expected to be an expert on any topic on day one. You have 3 (or maybe 6) years to learn what you need to know.
Comment: @Ian_Fin used to work with data migration before commencing the PhD
Comment: @SaberAlex It depends on the country you are in. In the UK it is not uncommon for people ending up working on far related subjects during their PhD. In other countries this is possibly less common from what I can see. Having said that, software engineering and data science are more closely connected than mathematics and (computational) chemistry...
Answer:
It's totally OK!

When it comes to PhD, enthusiasm, dedication and perseverance worth far more than prior knowledge and intelligence.
In fact, many of the people I know started their PhD without even knowing the slightest basics of their topic, but they excelled nonetheless.

This includes me. Since were in similar fields I suppose I could share my experience. I chose machine learning (ML) out of impulse because I was passionate about AI. I didn't even know the definition of ML when I started my PhD. Now, I'm recoding ML algorithms twisting them to my research needs. Moreover, I'm even teaching my students and colleagues to do the same. It's truly a magnificent experience.


Can anyone remember/name this sci-fi novel featuring the concept 'work is play'?

Question: I've been looking for it for maybe thirty years. Read it in the eighties in the US in English. Probably published in the eighties. Standard novel length, call it 120,000 words? It was a space opera-type novel that involved, in part, the concept of a world of humans that had learned to assign children to the specialty/career they were suited for and would regard as a form of play even as adults. It was not a YA novel, though. Mercenaries from this planet were the best because they "played" at war with that loose ease we all feel when we're playing a game we love. This world also produced the best diplomats, the best engineers, the best specialists of all varieties. The specialist from this world were in high demand all across the galaxy. This novel really struck a chord with me, but I can't remember the title or the author and haven't had any luck searching for it.
Comment: When did you read this book?  (We don't know how old you are; you might have read it 60 years ago.)  More to the point, do you have any idea when it was written (i.e., how old was it when you read it)?  What language was it in?  Where did you get/read it (i.e., what country)?  Can you estimate how long this book is?  There are thousands of books to go through, so anything that narrows it down will be helpful.  See also [our guidance](//scifi.meta.stackexchange.com/q/9335/30482) on asking good story-ID questions. … … … … … … … … … … … … … … … … … … P.S. I believe that you mean "struck a chord".
Answer: It is the Regiment series by John Dalmas, and the "Play" is a part of the Matrix of T'Sel. The book is available on Baen, I'll look up a blurb.
This phrase summarizes the Regiment philosophy:

For T'swa mercenaries, war was an activity as pure as healthy sex, and
  apparently as satisfying. Eventually, through death or wounds, they
  lost the ability to play at war any longer. That would happen to him
  with sex someday, through death or age or whatever.

This is the part in which the importance of Play is stated:

"Each T'swa warrior," Usu continued, "becomes a master at the art of
  war before his regiment is ever commissioned, and performs his art as
  perfectly as he is able, without distracting himself with concerns of
  victory or defeat, survival or death. The warrior at Fight will
  usually fall to him. And for just those reasons, our regiments enjoy
  great success."

There are some similarities between the T'swa philosophy/tech and some doctrines in which John Dalmas was said to dabble.