I have read "" but I'm still confused. How do I know when I should mark a variable volatile? What if I get it wrong, either omitting a volatile on something that needs it or putting volatile on something that doesn't? What are the rules of thumb when figuring out what variables should be volatile in multithreaded code?
At work today, I came across the volatile keyword in Java. Not being very familiar with it, I found . Given the detail in which that article explains the keyword in question, do you ever use it or could you ever see a case in which you could use this keyword in the correct manner?
The Lorentz force on a charged particle is perpendicular to the particle's velocity and the magnetic field it's moving through. This is obvious from the equation:  $$ \mathbf{F} = q\mathbf{v} \times \mathbf{B} $$  Is there an intuitive explanation for this behavior? Every explanation I've seen simply points at the equation and leaves it at that.  I can accept mathematically why $\mathbf{F}$ will be perpendicular to $\mathbf{v}$ and $\mathbf{B}$ (assuming the equation is correct, which it is of course). But that doesn't help me picture what's fundamentally going on.  Trying to create an analogy with common experiences seems useless; if I were running north through a west-flowing "field" of some sort, I wouldn't expect to suddenly go flying into the sky.  I'm hoping there's a way to visualize the reason for this behavior without a deep understanding of advanced theory. Unfortunately, my searching for an explanation makes it seem like something one just has to accept as bizarre until several more years of study. I know that the rotation period of the moon equals its revolution period. It's just so astonishing that these 2 values have such a small difference. I mean, what is the probability of these 2 values to be practically the same? I don't believe this to be a coincidence. It's just too much for a coincidence. What could have caused this? What's a common interjection for the reaction to something creepy and disgusting (like some insects or spooky places, etc.)? I recently found a formula to help find a sequence given a generating function:  $(\frac{1}{1-x})^k=\sum_{n=0}^{\infty}\binom{n+k-1}{n}x^n, k \in \mathbb{N}$  I just wondered if there was a known proof for this, or if anyone knows of a way to prove it. Finding an isomorphic subring of matrices GPS PPS signal corresponds to data time? I currently have an Adafruit Ultimate GPS connected to an Arduino that outputing GPS data (nmea sentences) once per second.  There is also a pin on the GPS outputting 1 PPS signal.    My question is whether the pulse of the PPS suppose to match the time that the GPS data is coming in i.e are they are coming in at the same time?    Also does PPS pulse come in at the beginning of a UTC second or is it random and simply once a second? Prevent iMac from sleeping, for VPN login? We have an iMac in the office, and I have been getting inconsistent access when trying to log in to it. The firewall isn't going down, since I can connect to the VPN. After discussing it with the people at the office, we suspect that the iMac is going to sleep.   Is it possible to keep the iMac "awake" 24 hours a day? How do I instruct the people at the office to configure the iMac? What settings should be changed? The iMac is running OS X Lion 10.7.3. Spacing around \left and \right Why does the addition of a \left and \right introduces an extra space around the formula? Specifically, why do $\cos(\theta)$ and $\cos\left(\theta\right)$ render differently?  Is there a way to use resizable delimiters without introducing the spurious spaces?  Why did Knuth design it like this?  Edit: This occurs too, if \operatorname{MYOP} or some other operator, like \lim, \min etc. is used. (This edit is basically to make it easier to find this answer.) I started by Time Series Analysis by Hamilton, but I am lost hopelessly. This book is really too theoretical for me to learn by myself.   Does anybody have a recommendation for a textbook on time series analysis that's suitable for self-study? Properties of $x_k=\frac{a_{k+1}-a_{k}}{a_{k+1}}$ where $\{a_n\}$ is unbounded, strictly increasing sequence of positive reals Let $\{a_n\}$ be an unbounded, strictly increasing sequence of positive real numbers and let $x_k=\frac{a_{k+1}-a_{k}}{a_{k+1}}$. Which of the following statements is/are correct? (CSIR NET December 2014)         For all $n\geq m, \sum\limits^{n}_{k=m}x_k&gt;1-\bf{\frac{a_m}{a_n}}$   There exist $n\geq m, \sum\limits^{n}_{k=m}x_k&gt;\frac{1}{2}$      My attempt:  Analysing question in light of $a_k=k\implies x_k=\frac{k+1-k}{k+1}=\frac1{k+1}$, I feel both are correct, I doubt if  I can generalise the result in light of this one example.   Any way to prove that this true for general case?    Note: Please do not confuse  with my question. The first two options are different, I've marked the difference in bold. Why and how is the speed of light in vacuum constant, i.e., independent of reference frame? I was told that the Galilean relative velocity rule does not apply to the speed of light. No matter how fast two objects are moving, the speed of light will remain same for both of them.   How and why is this possible?   Also, why can't anything travel faster than light? How can install Desktop Toggl on Ubuntu 13.04? I try type:  sudo add-apt-repository ppa:official-toggl/ppa sudo apt-get update sudo apt-get install desktop-Toggl    But getting information desktop-Toggl not found. Determining coordinates of a SHP file i have a SHP file of a building converted from a DXF file. This SHP file is unprojected and have no specific coordinates (origin 0,0). I find WGS84 coordinates (lat, long) of this building from Google Maps. My aim is to replace these coordinates to the SHP file on QGIS.  Could you explain the process step by step?  (I read lots of similar questions, about affine transformation. But i don't know the paramaters.)    What i ask is how to make this transformation in QGIS (step by step)?   SHP file coordinates (not projected)  Scale: 1:142.670.713  X1,Y1: 16.70824, 253.74534  X2,Y2: 1.03521,-6.34918  X3,Y3: 244.00248,-7.49189  Target WGS84 coordinates   X1,Y1: 41.047773, 28.896241  X2,Y2: 41.045452, 28.895929   X3,Y3: 41.045436, 28.899039    I need a second vector layer with coordinates. I have just a SHP file of a building converted from a DXF file. That is not projected. I know where this building is, and can find the WGS84 coordinates from Google Maps. My aim is add WGS84 coordinates to this SHP file and export to replace the building on Google Maps.  My Questions are:  1) I think my SHP file has measurements in meters and unprojected. I have WGS84 lat long coordinates from Google Maps. How can i project this SHP file, for being ready to transformation? Right Click -> Set Layer CRS -> Choose WGS84 EPSG: 4326. Is this enough?  2) qgsAffine plugin just need transformation matrix paramaters. But the answer of @Jochen Schwarze is a bit complex for me. Is there a online calculator? (Just give the source XYs and target XYs and calculate the parameters.)    I think, I have a projection problem before affine transformation. I have a DXF file of a building from AutoCAD. I saved this DXF file as a SHP file in QGIS. But this SHP file is converted from a plain DXF file and is not referenced/projected, it is drawn from coordinates 0,0 in AutoCAD in meters. And the drawing has meters, WGS84 has decimal degrees.  When I set Layer CRS as WGS84 in QGIS, the coordinates don't change.  How can I project this SHP file as WGS84 in QGIS? Show $\operatorname{rank}(A) + \operatorname{rank}(B) \ge \operatorname{rank}(A+B)$ Why does pdfTeX hang on this file? I have Ubuntu 12.04 installed on my PC, recently I have edited /etc/passwd  and changed  user1:x:00:00:user1,,,:/home/user1:/bin/bash   to give root permission to user1 and the system always need to login as root, for running some custom software.  Now it seems the sound is not working, the volume icon is disabled. I understand that the pulseaudio demon can't be run as root that's why the audio is not working. How can I resolve it, like set the permission of pulseaudio to run as root.   When I type the command    /usr/bin/pulseaudio --start   Giving me the output  W: [pulseaudio] main.c: This program is not intended to be run as root (unless --system is specified). E: [autospawn] core-util.c: Home directory /home/user1 not ours. W: [autospawn] lock-autospawn.c: Cannot access autospawn lock. E: [pulseaudio] main.c: Failed to acquire autospawn lock   Edit   Solution for problem:  I have fixed the problem by disable root checking for pulseaudio equalizer  sed -i 's/exit 1/#exit1/g' /usr/bin/pulseaudio-equalizer Is there an uncountable family of infinite parts of $\mathbb N$ with two to two intersection finite? What level is a spell if you cast it without expending a spell slot? There are ways to cast spells without expending a spell slot such as:  Master Transmuter (PHB 119):     Restore Life. You cast the raise dead spell on a creature you touch   with the transmuter’s stone, without expending a spell slot or needing   to have the spell in your spellbook.   Armor of Shadows (PHB 110):     You can cast mage armor on yourself at will, without expending a spell slot or material components.   Whispers of the Grave (PHB 111):     You can cast speak with dead at will, without expending a spell   slot.   See also: Channel Divinity: Read Thoughts (PHB 59-60), Mystic Arcanum (PHB 108), Beast Speech (PHB 110), Chains of Carceri (PHB 110), Eldritch Sight (PHB 110), Fiendish Vigor (PHB 111), Mask of Many Faces (PHB 111), Master of Myriad Forms (PHB 111), Misty Visions (PHB 111), Otherwordly Leap (PHB 111), Signature Spells (PHB 115), Spell Mastery (PHB 115), Shapechanger (PHB 119), Boon of Spell Mastery (DMG 232) and Boon of Spell Recall (DMG 232).  What level are these spells if you cast them without expending a spell slot? Do we need a global test before post hoc tests? I often hear that post hoc tests after an ANOVA can only be used if the ANOVA itself was significant.    However, post hoc tests adjust $p$-values to keep the global type I error rate at 5%, don't they?  So why do we need the global test first?  If we don't need a global test is the terminology "post hoc" correct? Or are there multiple kinds of post hoc tests, some assuming a significant global test result and others without that assumption? Is there a word to describe the virtue of "to do something and ask for nothing in return"? I am wondering if there is a positive, formal counterpart to the slang "No strings attached" to describe, for example, a parent's unquestioned devotion to their children, or the virtue of someone's "a friend in need is a friend in deed", help first, question later mentality.