Web based application requires a credit card to signup for a free 30 day trial account for which I have got mixed reviews, because application does not enforce any limit on the usage and companies like AWS already run on the model that requires credit card to signup of free 30 days trial.  What is the right user experience? Is having a credit card a mandatory thing to create a free trial?
In terms of UX what do you guys think is the best approach when integrating a trial period for subscriptions?  My application offers a 15 day trial, at the minute the user can sign up without providing any payment information (Paypal Subscription). The account is then set to trial status and after 15 days the user will be redirected to an upgrade page.  Do you think this is the best approach? I am unsure whether or not to let Paypal manage the trial, this however means that the user will need to go through the Paypal payment system during signup. I think this may put some people off signing up.  On the other hand this approach may increase the number of conversions to a full account.
Everyone knows that Wolverine's adamantium claws are super-sharp — sharper than even a razor — and virtually indestructible. What puzzled me the first time I saw Wolverine is: how do the claws stay in his body?  As it is shown, Wolverine's flesh and skin are human in strength, but the healing factor makes it superhumanly durable and strong. Still, when Wolverine slashes something, or someone, extremely hard, dense, or thick (as he has to use great amount of force), the claws don't tear through his hand and leave his hand through the opposite side of the palm (because of the action having equal and opposite reaction). Drush installed and running; No Drupal site found even with uri specified After much trial and tribulation, I thought I had drush all ready to roar. Much excitement. But then, no joy...  Drush is working. The sites operate fine via MAMP. Regardless, a "drush cc all" command returns:   No Drupal site found, only 'drush' cache was cleared.                                          [warning] 'all' cache was cleared.                                                                       [success]   This question has stumped drupalcon attendees and very experienced developers. Any ideas?  I am on Mac OS 10.9.3 using MAMP (free) Version 3.0.5  Here is my drush status:   Drupal version         :  7.29-dev                                 Site URI               :  http://default                           Database driver        :  mysql                                    Database hostname      :  localhost                                Database username      :  db_user                             Database name          :  db_name                        PHP executable         :  /usr/bin/php                             PHP configuration      :                                           PHP OS                 :  Darwin                                   Drush version          :  7.0-dev                                  Drush temp directory   :  /tmp                                     Drush configuration    :                                           Drush alias files      :                                           Drupal root            :  /Applications/MAMP/htdocs/mysite.dev   Site path              :  sites/default       Have tried executing drush from /Applications/MAMP/htdocs/mysite.dev; from /Applications/MAMP/htdocs/mysite.dev/sites/default; and using drush cc all --uri=http://localhost/mysite.dev  Tried running drush from sites/default. Same result. What is the difference between a neural network and a deep neural network, and why do the deep ones work better? I haven't seen the question stated precisely in these terms, and this is why I make a new question.  What I am interested in knowing is not the definition of a neural network, but understanding the actual difference with a deep neural network.  For more context: I know what a neural network is and how backpropagation works. I know that a DNN must have multiple hidden layers. However, 10 years ago in class I learned that having several layers or one layer (not counting the input and output layers) was equivalent in terms of the functions a neural network is able to represent (see Cybenko's ), and that having more layers made it more complex to analyse without gain in performance. Obviously, that is not the case anymore.  I suppose, maybe wrongly, that the differences are in terms of training algorithm and properties rather than structure, and therefore I would really appreciate if the answer could underline the reasons that made the move to DNN possible (e.g. mathematical proof or randomly playing with networks?) and desirable (e.g. speed of convergence?) how to set static ip from bash scriptlinux I want to set static IP using bash script what I would to achieve I want to set the same IP to static which is come from DHCP, for example, my eth0 set to DHCP and it picks IP 51.89.84.82 for eth1 it pick 10.0.0.1 I want to set the same IP to static how can I achieve this in centos7. 1 ) find interface name and its ip , subnet mask , gateway. 2 ) loop each interface and set the same ip , subnet and gateway. How do I bypass restrictions on the length of the PATH variable System Properties      This environment variable is too large. This dialog allows setting values up to 2047 characters long.   I use/have used a lot of software, and my PATH has grown as a result. When I try to add new paths, I get the above message. As a workaround, I'm editing my user path, but prefer not to. A doubt from Milnor's "Topology from a Differentiable Viewpoint". This is a doubt from Milnor's "Topology from a Differentiable Viewpoint".     For a smooth $f:M\to N$, with $M$ compact, and a regular value $y\in N$, we define $n(f^{-1}(y))$ to be the number of points in $f^{-1}(y)$. It is easy to see that $n(f^{-1}(y))$ is finite. It can also be seen that $n(f^{-1}(y))$ is locally constant; i.e. there is a neighbourhood of $y$ such that for every point $y'$ in that neighbourhood, $n(f^{-1}(y'))=n(f^{-1}(y))$.   The proof for the statement in bold is the following:     Let $x_1,x_2,\dots,x_n$ be the points of $f^{-1}(y)$, and choose disjoint neighbourhoods $U_1,U_2,\dots,U_n$ of these points, which are mapped diffeomorphically into neighbourhoods $V_1,V_2,\dots,V_n$ of $y$. The required neighbourhood is $(V_1\cap V_2\cap\dots V_n)-f(M-U_1-U_2-\dots U_n)$.   I don't understand how $(V_1\cap V_2\cap\dots V_n)-f(M-U_1-U_2-\dots U_n)$ is open. I know that $(V_1\cap V_2\cap\dots V_n)$ is open. However, how can one prove that $f(M-U_1-U_2-\dots U_n)$ is closed? I can see this working if $f$ is surjective, but not otherwise. How can I automatically name files being exported based on input parameters Does disabling root login enhance security? I'm just starting to learn linear algebra and I understand Gaussion elimination but I don't understand this proof:    Is the heart of this the fact that all the while when I've been row-reducing matrices to reduced row-echelon form... I've actually been multiplying a matrix by a series of a elementary matrices?  What does the notation $[A\ \ 0]$ mean?  How is the equation $A = E_1^{-1}...E_k^{-1}$ arrived at? SEO (or other) problems with a 404? Are all multiplicative functions additive? Suppose $cf(x)=f(cx)$ and $f:\mathbb{R}\to\mathbb{R}$. I believe it follows that $f(x+y)=f(x)+f(y)$.   Proof: There is some $c$ such that $y=cx$. Then  $$f(x+y)=f\left((1+c)x\right)=(1+c)f(x)=f(x)+cf(x)=f(x)+f(cx)=f(x)+f(y)$$  QED.  I wonder if the same thing holds for when $f:\mathbb{R}^n\to\mathbb{R}^n$? I can't use the same trick, because all vectors are not scalar multiples.  I tried thinking of it in terms of basis units, but didn't get anywhere. Cannot install Oracle JDK via apt in Ubuntu 16.04 I created a new Ubuntu 16.04.3 VM and am attempting to install JDK 9. Unfortunately, the latest version of the JDK apt installer, 9.0.1-1~webupd8~0, is failing to download the binaries and I suspect that the reason is because   I carried out the typical steps for installation:    add-apt-repository ppa:webupd8team/java apt-get update &amp;&amp; apt-get install oracle-java9-installer   I am then prompted with the following error message:  Downloading Oracle Java 9... --2018-01-16 15:15:07--  http://download.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz Resolving download.oracle.com (download.oracle.com)... 23.200.70.136 Connecting to download.oracle.com (download.oracle.com)|23.200.70.136|:80... connected. HTTP request sent, awaiting response... 302 Moved Temporarily Location: https://edelivery.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz [following] --2018-01-16 15:15:11--  https://edelivery.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz Resolving edelivery.oracle.com (edelivery.oracle.com)... 23.35.226.115, 2600:1404:21:49d::2d3e, 2600:1404:21:493::2d3e Connecting to edelivery.oracle.com (edelivery.oracle.com)|23.35.226.115|:443... connected. HTTP request sent, awaiting response... 302 Moved Temporarily Location: http://download.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz?AuthParam=1516137431_0e89d10b30203a572ea858768475ef74 [following] --2018-01-16 15:15:11--  http://download.oracle.com/otn-pub/java/jdk/9.0.1+11/jdk-9.0.1_linux-x64_bin.tar.gz?AuthParam=1516137431_0e89d10b30203a572ea858768475ef74 Connecting to download.oracle.com (download.oracle.com)|23.200.70.136|:80... connected. HTTP request sent, awaiting response... 404 Not Found 2018-01-16 15:15:11 ERROR 404: Not Found.  download failed Oracle JDK 9 is NOT installed. dpkg: error processing package oracle-java9-installer (--configure):  subprocess installed post-installation script returned error exit status 1 Errors were encountered while processing:  oracle-java9-installer E: Sub-process /usr/bin/dpkg returned an error code (1)   I found , but it does not appear that the  works for JDK 9.0.4+11. I've updated the SHA checksums (), set the major version to 9.0.4, and set the minor version to 11, but I'm still not having success.  What steps need to be carried out to get the JDK apt installer to work until the WebUpd8 team is able to update the PPA? Benchmark (hash rate) for SHA-3 (SHAKE128) To estimate the time for brute-force attack we need to compute keyspace size divided by hash rate, where the hash rate (hash/second) varies depending on the computer's capabilities.  The website  shows the hash rate for different computers.  Can you explain the following two confusing phenomena?   The hash rate decreases as the message size increases. Core i3 has a higher hash rate than Core i7 for SHAKE128. Operator font in beamer/metropolis When using the metropolis theme for beamer, I get text and math in Fira Sans, except for math operators. I compile the following MWE using LuaTeX.  \documentclass{beamer}  \usetheme{metropolis}  \begin{document}    \begin{frame}     Ordinary text.     \[ a^2 + b^2 = \sin^2(x) - \mathsf{y} + \mathrm{z}  \]   \end{frame}  \end{document}   The outcome for me is that a, b, 2 and x are set in Fira Sans Light Italic, and y is set in Fira Sans Light, but sin is set in the sans font of (I guess) Latin Modern. (The z is also in Latin Modern, but this is expected behaviour from beamer.)  Unsurprisingly, I get the same result if I replace \usetheme{metropolis} with  \usepackage[no-math]{fontspec} \setsansfont[ItalicFont={Fira Sans Light Italic},   BoldFont={Fira Sans},   BoldItalicFont={Fira Sans Italic}]%   {Fira Sans Light}   I guess that this is to do with beamer's patching parts of the math fonts to match the text font (see ). However, I don't understand the font system well enough to modify this.  There was , but I've no idea how to apply that answer when using fontspec, or if this is even possible.  Is there a way to change the operator font to match the upright/sans math font (i.e., Fira Sans Light)? Multiple monitors, multiple workspaces? I connected my laptop to my LCD. Using the laptop display hotkey I can switch between different modes - only laptop monitor on, only LCD monitor on, both on and display the same view, both on and the desktop is stretched (divided).  But, I'm looking for something else - I would like to have two workspaces, one visible on the laptop monitor and the other on the LCD.  Is that possible? What kind of "mathematical object" are limits? How can I format a date as dd/mm/yyyy or mm/dd/yy ?   Like in VB format("dd/mm/yy",now)  How can I do this in C#? As a result of  myself, the need arose to track other Stack Overflow-based research. The following is an attempt to list the academic papers mentioning Stack Overflow/Exchange or using Stack Exchange data. This also includes the works mentioned in  that started the trend, as well as two other questions on meta, , and . If you know of papers that are not listed, please edit the answer directly. I realised it might be useful to have all the BibTeX entries in a single file, so I started . Proof that a sequence is convergent Posts linked in deleted answers still show up under "Linked" E.g. see .