Can we find the derivative of modulus function? if yes, then how?
Derivative of $f(x)=|x|$
Please add the ability to fold blocks of code in questions and answers It would be great to have the option to fold code snippets, entire questions and answer posts on a user basis and allow defining some generic foldable regions within the question/answer editor.  Non generic folding info could be stored in cookies perhaps to move the storage/processing requirement to the client side.  Definable folding can take any free and safe HTML tag or other multi character trick (&lt;>Fold this&lt;>) Get referenced node fields in twig What is the best technique for long-exposure photography in good light? How to sum 2 vectors in spherical coordinate system There have been several questions already posted with specific questions about , such as when to use it and what frameworks are there for it. However,  What is dependency injection and when/why should or shouldn't it be used? QGIS 3.4 : Add points to exact locations? I would like to add several coordinates at specific British National Grid Easting and Northing values. I know this can be done by bringing in a .csv, but I want to know is there a way to manually enter the numbers in QGIS 3.4, and then the point moves to that location ? I've read that in QGIS 2.x there was a plugin called Numerical Vertex Editor that doesn't seem to exist for 3.x ? Difference between StringBuilder and StringBuffer Wired connection not working Ubuntu 12.04 List of GUI Based Torrent clients Evaluate  $$\int_0^\infty \frac{\log x \; dx}{x^{2} + 2x + 2}$$  by integrating a branch of $(\log z)^{2}/(z^{2} + 2z +2)$ along a keyhole contour.  The thing I have trouble with is why I should be examining the square of the log - I guess it has something to do with ln x in fact NOT being the real part of log z, since log z is (or can be) defined on the entire negative real axis and ln x can't. But looking at the square would definitely not have been my first plan of attack :( How to change Status Bar text color in iOS Terminal prompt overwrites current line Do I need an ESTA to enter the US with the Victoria Clipper ferry? I am thinking of visiting Victoria, BC in Canada and then going to Seattle, WA in the US, with the .  I am a national of a country under the Visa Waiver Program. I think that if I enter by air, I need to fill an ESTA form. If I enter by car, I don't need one, I can fill a form when crossing the border.  With the ferry, what is the procedure? Should I necessarily have an ESTA? undelete big files - mission impossible? I've accidentaly deleted outlook.pst (6.7GB) file, while there was only 400MB free space left on primary NTFS partition (winxp).  I've tried several recovery tools to get this file back. "Ontrack Easy Recovery Pro" found 0 pst files (complete scan mode), while "Recover My Files" in sector scan mode found 5 pst's, but 4 of them of sizes from 3 to 28 KB, while the 5th one - 1Gb.  I've managed to succesfuly recover 1Gb pst file, which was 1 year old copy (the one used after the latest windows reinstall).  Now, I'm frustrated and confused   Why 1 year old file was succesfuly recovered if there were only 400MB left on primary partition? Where's 6.7GB file gone? I did some reading (), and it seems that there's almost no probability to retrieve the file I'm looking for, but wait - none of recovery tools i've used found zero-sized pst file, moreover - if due to fragmentation a file might be corrupted - we could use scanpst.exe to fix some errors and survive with 10 or 100 emails missing - whatever. Could you please recommend some more sophisticated recovery tools for this particular task?   Appretiate your help - thanks in advance How to convince longtable to do a page break earlier using the longtable package to typeset page spanning tables, I run into a nasty behaviour: only a dummy table head and the caption are put on the following page. The contents of the table is extracted from program sources. I don't have much influence here.  \documentclass[a4paper,twoside,DIV10,BCOR1.5cm]{scrbook} \usepackage{longtable} \newlength{\tablcol} \setlength{\tablcol}{4.7cm} \newlength{\tabrcol} \setlength{\tabrcol}{8.1cm} \itemsep0ex plus0.2ex % \begin{document} \begin{longtable}{p{\tablcol}p{\tabrcol}}% % \hline \multicolumn{1}{l}{{\bfseries Feld}} &amp; \multicolumn{1}{l}{{\bfseries Beschreibung}}\\ \hline \endfirsthead % \hline \multicolumn{2}{l}% {{\small\slshape Fortsetzung der vorherigen Seite}}\\ \hline \multicolumn{1}{l}{{\bfseries Feld}} &amp; \multicolumn{1}{l}{{\bfseries Beschreibung}}\\ \hline \endhead % \hline \multicolumn{2}{l}% {{\small\slshape Fortsetzung auf der n\"achsten Seite}}\\ \hline \endfoot % \hline \caption[show user output]{Beschreibung der Output-Struktur des show user Statements} \endlastfoot % \label{tucshowxuser}% {\scshape id} &amp; Die Nummer des Repository Objektes \\ {\scshape name} &amp; Der Name des Objektes \\ {\scshape creator} &amp; Name des Benutzers der dieses Objekt angelegt hat \\ {\scshape create\_time} &amp; Datum und Uhrzeit der Erstellung \\ {\scshape changer} &amp; Name des Benutzers der dieses Objekt zuletzt ge\"andert hat \\ {\scshape change\_time} &amp; Datum und Uhrzeit der letzten \"Anderung \\ {\scshape privs} &amp; Zeichenkette die K\"urzel f\"ur die Benutzerrechte auf dieses Objekt enth\"alt \\ {\scshape commenttype} &amp; Typ des Kommentars \\ {\scshape comment} &amp; Kommentar zum Objekt, wenn vorhanden \\ {\scshape id} &amp; Die Nummer des Repository Objektes \\ {\scshape name} &amp; Der Name des Objektes \\ {\scshape creator} &amp; Name des Benutzers der dieses Objekt angelegt hat \\ {\scshape create\_time} &amp; Datum und Uhrzeit der Erstellung \\ {\scshape changer} &amp; Name des Benutzers der dieses Objekt zuletzt ge\"andert hat \\ {\scshape change\_time} &amp; Datum und Uhrzeit der letzten \"Anderung \\ {\scshape privs} &amp; Zeichenkette die K\"urzel f\"ur die Benutzerrechte auf dieses Objekt enth\"alt \\ {\scshape commenttype} &amp; Typ des Kommentars \\ {\scshape comment} &amp; Kommentar zum Objekt, wenn vorhanden \\ {\scshape id} &amp; Die Nummer des Repository Objektes \\ {\scshape name} &amp; Der Name des Objektes \\ {\scshape creator} &amp; Name des Benutzers der dieses Objekt angelegt hat \\ {\scshape create\_time} &amp; Datum und Uhrzeit der Erstellung \\ {\scshape changer} &amp; Name des Benutzers der dieses Objekt zuletzt ge\"andert hat \\ {\scshape change\_time} &amp; Datum und Uhrzeit der letzten \"Anderung \\ {\scshape privs} &amp; Zeichenkette die K\"urzel f\"ur die Benutzerrechte auf dieses Objekt enth\"alt \\ {\scshape commenttype} &amp; Typ des Kommentars \\ {\scshape comment} &amp; Kommentar zum Objekt, wenn vorhanden \\ {\scshape id} &amp; Die Nummer des Repository Objektes \\ {\scshape name} &amp; Der Name des Objektes \\ {\scshape creator} &amp; Name des Benutzers der dieses Objekt angelegt hat \\ {\scshape create\_time} &amp; Datum und Uhrzeit der Erstellung \\ \end{longtable}  \end{document}   The problem is that I don't find a method to force a page break earlier. A page that isn't filled entirely, followed by a page with the last part of a table is better than this.  I tried to add "\needspace{someLength}" at the beginning or end of the rows, but that doesn't work either. It simply makes the rows someLength high instead of forcing a page break if there's no more than someLength room left on the page.  I'd be more than grateful for some solution or even a good hint.  TIA How does "warp drive" not violate Special Relativity causality constraints? I'm talking about this nonsense:   Now, I'm aware that there are problems with the practicalities (or possibilities) of methods involving exotic matter with negative mass, and that kind of thing has been addressed here:   But in this case my question is different and more specific. Sweeping all the other problems of constructing such a beast under the rug, wouldn't this violate causality?  SR says that the simultaneity and relative ordering of events is dependent on the relative motion of the observer, but that no matter how it works out, if event A causes event B, no observer will see B first. One of the many problems with FTL travel (or signals) is that if any information is sent faster than light, there will exist an inertial frame in which the signal arrives before it is sent, a blatant violation of causality. (I think we can all agree, can we not, that the threshold should be extremely high before breaking assumptions that we're in a causal universe?)  So how is any scheme to travel faster than light, even if it may locally satisfy the equations of GR, not a blatant violation causality according to SR?  Is my understanding of GR incomplete and there's something in it that obviates the causality implications of SR? Or am I correct that FTL claims should be dismissed with extreme prejudice on this basis alone? (Pending a serious replicable experiment showing causality to be breakable.) Outlook: scheduling recurring out-of-office? In Outlook, is there a way (or an add-on that can do it) to schedule a recurring out-of-office message?  I work 4 10's, so I'm out of the office every Monday, and it's a bit of a pain to have to reset my out-of-office message every single week. How to use `ybar interval` without skipping the last value Allow the owner of a post to approve a suggested edit even if it was rejected by reviewers How would one denote the set of all subsets of $A$ which have size $2$?  Would  $$\binom{A}{2}$$  be a good idea?