Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference in Android
What is a NullPointerException, and how do I fix it?
If $f$ is a periodic function with $T = \pi$, does that mean that $F$ (a primitive of $f$) has the same period ? What about the inverse implication (periodic primitive implies periodic function) ? Can't deep learning models now be said to be interpretable? Are nodes features? For statistical and machine learning models, there are multiple levels of interpretability: 1) the algorithm as a whole, 2) parts of the algorithm in general 3) parts of the algorithm on particular inputs, and these three levels split into two parts each, one for training and one for function eval. The last two parts are much closer than to the first. I'm asking about #2, which usually leads to better understanding of #3). (if those are not what 'interpretability' means then what should I be thinking?)  As far as interpretability goes, logistic regression is one of the easiest to interpret. Why did this instance pass the threshold? Because that instance had this particular positive feature and it has a larger coefficient in the model. It's so obvious!  A neural network is  the classic example of a model that is difficult to interpret. What do all those coefficients mean? They all add up in such complicated crazy ways that it is hard to say what any particular coefficient is really doing.  But with all the deep neural nets coming out, it feels like things are becoming clearer. The DL models (for say vision) seem to capture things like edges or orientation in early layers, and in later layers it seems like some nodes are actually semantic (like the proverbial ). For example:    ()  This is a graphic () created by hand for presentation so I am very skeptical. But it is evidence that somebody thinks that is how it works.  Maybe in the past there just weren't enough layers for us to find recognizable features; the models were successful, just not easy to post-hoc analyze particular ones.  But maybe the graphic is just wishful thinking. Maybe NNs are truly inscrutable.  But the many graphics with their nodes labeled with pictures are also really compelling.    Do DL nodes really correspond to features? May I summarize all answers on StackOverflow, I asked a . There are many good answers but I can not accept just one of it. I would prefer to create my own answer where I summarize all answers. Is that allowed? Can you trip as part of a Tome of Battle Maneuver? If a ToB Maneuver such as Daunting Strike calls for a melee Attack as part of the maneuver, can this melee attack be resolved as a trip attack/include a trip attempt? I know the past tense carries the past tense in every dependent clause, but referring specifically to places or to things that are eternal, like the Earth, seems a bit weird and therefore we sometimes (I believe incorrectly) say     He didn't know that New Jersey was actually on the East Coast.   Because it still is. Or     He thought the Earth was round.   So is it square now?  Logically speaking, would you consider the use of past tense here a bit confusing in a day-to-day speech in these examples? Would you instinctively opt for using the present tense? How can one show there is no holomorphic function $f$ on the open unit disc $\mathbb{D}$ such that it extends continuously to $\frac{1}{z}$ on $\partial\mathbb{D}$? I mean $f$ takes value $\frac{1}{z}$ when $|z|=1$ and continuous here.  Thank you. Berlin Public Transport Ticket Validity I have purchased an AB zone Berlin 7 day transport ticket and validated it on Sunday 17th April so hopefully it will be valid until Sunday 24th.  I validated the ticket at about 10:00am so I guess 1000 is the time I validated? But what are the numbers 15 and 6 and letters 'So' correspond to? How (if checked by a guard) can they tell if the ticket is valid? And how can I as a customer tell when it is validated to? The Complete Rate-Limiting Guide I noticed that I can only perform certain actions such as commenting a finite number of times in a given period of time. Obviously, rate limiting is in place to prevent accidental misuse or intentional abuse of certain features.  Where else is rate limiting applied on Stack Exchange sites, and what are the limits? Can someone give me an example for this question on reflexivity please. How is this reflexive? Can you show an example with numbers from the set?     Question 6   Let $X = \{0,1,2,3,\dotsc, 9\}$. Define a relation $\mathcal R$ from $X$ by "$x$ is related to $y$ if $x$ and $y$ gives the same remainder on division by $3$".   (a) Show that $\mathcal R$ is an equivalence relation.   Anwser:   (a) $\mathcal R$ is clearly both reflexive and symmetric, for every number has the same (unique) remainder on division by $3$ as itself and if $a$ has the same remainder on division by $3$ as does $b$, then $b$ has the same remainder on division by $3$ as $a$ also. Similarly $\mathcal R$ is transitive, for if $a\mathcal R b$ and $b\mathcal R c$, then $a$, $b$, and $c$ all have the same remainder on division by $3$, so $a\mathcal R c$ also. I'm running CentOS 7.0 build 1503. I'm trying to search for commands I don't know the name of by searching the man descriptions for multiple keywords using AND (e.g. search for a command containing the both words "create" and "group" in the description).  So I came across the command apropos (which is an alias for man -k). The default behaviour when given multiple keywords is to return any command matching any of the keywords, which isn't what I want. According to the man page the option -a specifies using AND, to return matches only when all words match.  But this isn't what I'm seeing in practice, so I need some help here - e.g. using Centos 7, if I do:  apropos create user   I see a huge list of commands, seemingly matching any command with create or user in the description, as expected. Noting the list includes an entry for the command 'useradd (8) - create a new user...'.  If I do:  apropos -a create user   I only get 2 commands (environ and open). This is what I'm confused by - I would expect it to return the command 'useradd (8) - create a new user', because i can see from the previous search that command does contain those words in the description. Also the 2 returned commands don't obviously seem to be anything about creating users. What am I doing wrong? I'm sure it's something embarrassingly obvious, for that I apologise in advance.  Thanks I replaced a buggy Windows Vista installation with Ubuntu. All works fine except that the main HD where I had all my files are now inaccessible. Here is the error message I get:   Error mounting: mount exited with exit code 13: ntfs_attr_pread_i: ntfs_pread failed: Input/output error Failed to read NTFS $Bitmap: Input/output error NTFS is either inconsistent, or there is a hardware fault, or it's a SoftRAID/FakeRAID hardware. In the first case run chkdsk /f on Windows then reboot into Windows twice. The usage of the /f parameter is very important! If the device is a SoftRAID/FakeRAID then first activate it and mount a different device under the /dev/mapper/ directory, (e.g. /dev/mapper/nvidia_eahaabcc1). Please see the 'dmraid' documentation for more details   Is it necessarily a hardware problem? If not, is there a way to repair the HD from Ubuntu? Is there a route that would allow travel to the US from the UK or Schengen area, given the US travel ban? I'm a European citizen living in the US on a work visa. Due to some unfortunate circumstances, I need to urgently visit my home country. However I would like to get back to the US after my visit is complete. Flying from the US to Europe is not a problem as there are still daily flights between some city pairs. However going back could be tricky, as  anyone who has been in the Schengen area in the past 14 days from re-entering the country.   Is there a flight route that would let me from Europe to some country, stay there for 14 days and then fly to the US? Canada is out, as they've banned international visitors. Mexico seems to keep their border open, but I  any direct European flights from their airports. Almost every other country either suspended flights or doesn't allow foreign nationals to enter. What's the difference between "cd ../" vs. "cd /.."? What's the simplest way to call Http GET url using Delphi? There's a web services I want to call in my application, I can use it with importing the WSDL or by just use "HTTP GET" with the URL and parameters, so I prefer the later because it's simple thing.  I know I can use indy idhttp.get, to do the job, but this is very simple thing and I don't want to add complex indy code to my application.  UPDATE: sorry if I was not clear, I meant by "not to add complex indy code", that I don't want add indy components for just this simple task, and prefer more lighter way for that. What is "Best Practice" For Comparing Two Instances of a Reference Type? I came across this recently, up until now I have been happily overriding the equality operator (==) and/or Equals method in order to see if two references types actually contained the same data (i.e. two different instances that look the same). I have been using this even more since I have been getting more in to automated testing (comparing reference/expected data against that returned). While looking over some of the  I came across an  that advises against it. Now I understand why the article is saying this (because they are not the same instance) but it does not answer the question:  What is the best way to compare two reference types? Should we implement ? (I have also seen mention that this should be reserved for value types only). Is there some interface I don't know about? Should we just roll our own?!  Many Thanks ^_^ Update Looks like I had mis-read some of the documentation (it's been a long day) and overriding  may be the way to go..  If you are implementing reference types, you should consider overriding the Equals method on a reference type if your type looks like a base type such as a Point, String, BigNumber, and so on. Most reference types should not overload the equality operator, even if they override Equals. However, if you are implementing a reference type that is intended to have value semantics, such as a complex number type, you should override the equality operator. Beamer, Babel and Tikz conflict I am using &lt;a&gt; tags for links on a web page. How do I disable the Tab key from selecting either of them? Possible arguments:  Pro   For brevity for trivial deductions   Contra   Looks like the writer could not be bothered to write an extensive explanation Definition of what is trivial to which reader and what not Best way to include pdfs in an app Removing extra page before and after \tableofcontents My main file generate extra page before \tableofcontents with header title "Table of contents". How can I remove this page?  I am copying the main.tex file code for your reference.   \documentclass[twoside,12pt]{Classes/aesm_edspia}  \begin{document} \addtocounter{page}{-1} \makethese  \onehalfspacing \newpage\thispagestyle{empty}\addtocounter{page}{-5}   %depth in the table of contents and section numbering \setcounter{secnumdepth}{3} \setcounter{tocdepth}{3} \frontmatter  \pagestyle{fancy} \fancyhf{} \fancyhead[LE,RO]{Acknowledgements} \fancyfoot[RO]{\thepage} \fancyfoot[LE]{\thepage} \renewcommand{\headrulewidth}{0.5pt} \renewcommand{\footrulewidth}{0pt}  \pagestyle{fancy} \fancyhf{} \fancyhead[LE,RO]{Table of Contents} \fancyfoot[RO]{\thepage} \fancyfoot[LE]{\thepage} \renewcommand{\headrulewidth}{0.5pt} \renewcommand{\footrulewidth}{0pt}  \input{Abstract/Abstract}  \tableofcontents \listoffigures \listoftables   \mainmatter \pagestyle{fancy} \fancyhf{} \fancyhead[LE,RO]{Introduction} \fancyfoot[RO]{\thepage} \fancyfoot[LE]{\thepage} \renewcommand{\headrulewidth}{0.5pt} \renewcommand{\footrulewidth}{0pt}   \end{document}