Using Lagrangian mechanics instead of Newtonian mechanics
What is the difference between Newtonian and Lagrangian mechanics in a nutshell?
What is the meaning of "this" in Java? How to find the number of anti-symmetric relations? How do I  prevent .xsession-errors from eating disk space? Why doesn't \makeatletter work inside \newcommand? After hours of banging my brain against my skull, I narrowed down an issue I'm having to the fact that \makeatletter doesn't work inside \newcommand. Commands that I call after \makeatletter are registered as undefined, as if \makeatletter didn't do anything.  Why is this the case?  In the example below, I define two commands. Calling one of them from the document body causes the undefined error, while the other doesn't.  \documentclass[11pt]{book} \usepackage{kvsetkeys}  \newcommand{\commandThatFails}{     \makeatletter \comma@parse{}{} \makeatother }  \makeatletter     \newcommand{\commandThatWorks}{         \comma@parse{}{}     } \makeatother  \begin{document}  Hi there.  \commandThatFails \commandThatWorks  \end{document} How To Make Clickable Text In Minecraft I am trying to make clickable text in Minecraft in the chat box. It was used in the adventure map, "UP".   The idea is that you are given an option in the text to click, "Yes", or "No". Each word will give an output of a command.  How is this achieved? How to add click event to an element? How to setup a restricted SFTP server on Ubuntu? I would like to know how to set up root, sudo, sftp-only user accounts which won't be required public key authentication at log in. I would also like to know how to set up sftp-only users' home directories where they can't access upper level other directories. Picking a lock typically requires a DC 15 Dexterity check (Basic rules, p. 49). Likewise for manacles (p. 50), which can alternately be escaped with a DC 20 Dexterity check or broken with a DC 20 Strength check. But what happens if you fail?  The general rules for ability checks state (p. 58):     If the total equals or exceeds the DC, the ability check is a success—the creature overcomes the challenge at hand. Otherwise, it’s a failure, which means the character or monster makes no progress toward the objective or makes progress combined with a setback determined by the DM.   As a DM, how can I handle this in practice? In our last session, the players wanted to get inside a locked building to rescue people trapped inside. Picking the lock seemed like an easy enough task for the rogue, but unluckily he failed the check, and I wasn’t prepared for the consequences. There wasn’t much time pressure and no obvious reason why he couldn’t try again, so I allowed another attempt, but it just didn’t feel right.  I’m sure that similar situations will come up again, so I’d like some advice on how to deal with checks so that they don’t just turn into a tedious exercise of rolling until you succeed. I presume that  was left out of the game for good reason, but I’m not sure what to do instead. I suspect that this was a good occasion to use “progress with a setback” but that’s a fairly new thing for D&amp;D and I’m not sure how to go about it. I’m unsure when I should use setbacks versus lack of progress, and in the latter case I’m unsure when I should allow players to try again versus requiring a different approach.  For example, suppose that a manacled player tries to pick the lock and fails the DC 15 Dexterity check. Now, the player could try to pick it again, or he could try one of the other escape methods, or he could wait for somebody else to rescue him, or he could simply succeed with some setback like a minor injury. How do I choose how to proceed? Or do I let the players choose? How were the solar masses and distance of the GW150914 merger event calculated from the signal? How to kill a player when they touch a block? I am making a multiplayer parkour map on bedrock edition, and I have it set up where when a player steps on a grass block they die. But when a player steps on a grass block it just kills anyone who touches it.  First: A repeat command block (set to always active and unconditional)   execute @e [type=player] ~ ~ ~ testforblock ~ ~-1 ~ grass   And then I have a chain command block (set to conditional and always active)  kill @e [type=player]   And it does work..... IF in singleplayer only. (which is not at all what I want)  Thank y'all in advance. How can I turn off the shrine indicator (or make it stop beeping)? Rotation of braces How can I rotate a brace to make it appear ?  I'm currently using this code:  \documentclass[french]{beamer} \usepackage{tikz} \usetikzlibrary{fit,calc,positioning,decorations.pathreplacing,matrix} \begin{document} \begin{frame} \begin{tikzpicture}[decoration={brace}][scale=2]  \node [rotate=270] (A) {\fontsize{8}{8}\selectfont A};  \node [fit=(A)] (fit) {};               \draw [decorate,line width=1pt]    ([yshift=7pt]fit.south west) -- ([yshift=-7pt]fit.north west); \end{tikzpicture} \end{frame} \end{document}   Thanks in advance! Why do some font commands behave differently? I've always been confused by the differences in behavior of font commands.  For example, we have \mathrm{} and \texttt{}, which can be used like this: \texttt{hello} world.  And then we have \it and \bf which must be used as {\it hello} world. If one uses \it{hello} world, both words are italicized.  Internally, what is the difference here? And was this difference a conscious design decision? If so, why? Redefining "cited on" string (and others) in biblatex I'm trying to modify the strings biblatex uses to set the "cited on" string used in the bibliography to identify the pages where a given references has been cited.    What I gather from the biblatex documentation (e.g., § 4.9.2.16) is that something like   \renewbibmacro{backrefpage}{&lt;newtext&gt;} \renewbibmacro{backrefpages}{&lt;newtext&gt;}   ought to work, but they have no effect for me (I'd also like to get this working for the "visited on" string, urlseen).  My MWE is unchanged from , with the addition of these (and related lines) just about anywhere. I have been having a discussion regarding the Shape Water cantrip from the Elemental Evil Player's Companion. A friend and I are trying to come to an accurate view of how this spell actually functions.   Some example questions:   Must the targeted water be within a 5 foot cube area, or does it need to be of a volume not exceeding 125 cubic feet? If you shape water that is within a 5 foot cube, can the final shape you animate it to extend outside the cube? Can you cause the shaping to affect ice and snow, or only liquid water? Would you be able to carry a globe of water alongside you over distances?   Really, there are two parts:    What can be targeted by the spell? What are the limitations on the 'shape and animate' portion of the spell?   The answer I am looking for, if possible, would use the language of the spell, possibly with precedent from other game text, to clearly define the limitations of this cantrip. What should I consider when choosing continuous lighting vs. strobes for studio photography? How does PK know better than Jaggu? Do I need a Schengen visa if I have UK permanent residency? Table of Contents with Chapter I'm attempting to modify the Table of Contents in my document. Currently, chapter one in my document is listed as   1   Introduction   What I would like to see is  Chapter 1   Introduction   Seems like an easy enough thing to ask for, but can't seem to find a good way to do this. Any feedback would be most appreciative. Relativistic speed/energy relation. Is this correct?