Microcontroller and processor same thing or not?
What's the difference between a microcontroller and a microprocessor?
String.split() *not* on regular expression? Trying to open a http website on any web browser (event telnet) gives a ‘ERR_CONNECTION_REFUSED’ or ‘connection timed out’.  However, the same sites can be opened using https. I tried doing a traceroute and it works fine.  I am new to OS X but have experience with Linux. How do I go about troubleshooting this issue?  Update  I think I've tracked down the culprit to a rule in pf (firewall).  The result of sudo pfctl -s nat is:  No ALTQ support in kernel ALTQ related functions disabled rdr pass inet proto tcp from 192.168.0.101 to any port = 80 -&gt; 127.0.0.1 port 9882   192.168.0.101 is the current ip address of the computer.  I tried to remove the rule with sudo pfctl -F all, but it is back after a few seconds. I didn't find the rule in the default configurations (/etc/pf.conf). And disabling pf with sudo pfctl -d has no effect on it.  Is this a malware issue? Partition of a set and Hall's theorem Bold row in table aligned with dcolumn If I add a comment but navigate (by mistake) to another page, I lose my unfinished comment (ok, depends on browser etc). On the other hand, when formulating a question, and I click on a link by mistake, I'm asked if I really want to leave.  It would be nice to have this warning for comments as well. How can I insert a newline in a framebox? I have several frameboxes in my document, using the following command:  \framebox(115,115){ R-Sq: \newline For example}    I want to force a new line, but neither \newline or \\ appear to work. Is there any other way of doing this? Proof by induction on a rooted tree with even number of vertices Let $T = (V, E)$ be a rooted tree with an even number of vertices. Prove by induction that there exists a set of edges $S \subseteq E$ such that every $v \in V$ is incident with an odd number of edges in $S$.  I was wondering if my argument is sufficient to prove the statement above:  Base case: $|V|=2$, there is only 1 edge and both vertices are incident with 1 edge $-&gt;$ $S \subseteq E$.  Inductive step:  Let $|V|&gt;2$, implying that $T$ has at least 2 external vertices. Let us choose two arbitrary external vertices $w,u \in V$. Such vertices are only incident to 1 edge each, $e_w$ and $e_u$. We can say that $e_w,e_u \in S$.   By induction, there exists a set $S$ in $T'=T-\{w,u\}=(V',E')$ such that every $v \in V'$ is incident with an odd number of edges in $S$ because removing 2 vertices from a tree with an even number of vertices maintains the property $|V|=2n$. On the grade of an ideal I need to prove the following statment (actually a special case of it).     Let $R$ be a Noetherian ring, $M$ a finite $R$-module and $I$ an ideal of $R$. Then   $\operatorname{grade}(I,M)\geq 2$ if and only if the homomorphism $M\rightarrow$Hom$_R(I,M)$ given by $m\mapsto(i\mapsto im)$ is an isomorphism.   This is Exercise 1.2.24 in Bruns and Herzog, Cohen-Macaulay Rings. MySQL strip non-numeric characters to compare I'm looking to find records in a table that match a specific number that the user enters.  So, the user may enter 12345, but this could be 123zz4-5 in the database. I imagine something like this would work, if PHP functions worked in MySQL. SELECT * FROM foo WHERE preg_replace(&quot;/[^0-9]/&quot;,&quot;&quot;,bar) = '12345'  What's the equivalent function or way to do this with just MySQL? Speed is not important. Given Ohm's law, how can current increase if voltage increases, given fixed resistance? According to Ohm's law, $V=IR$ (voltage equals current times resistance).  So if the voltage increases, then the current increases provided that the resistance remains constant.  I know that Voltage or potential difference means work done per unit positive charge in bringing that charge from one point to another.  So according to Ohm's law, if the work done per unit charge increases then current will increase. How can this be true? Point out my mistakes. How can I optimise a Minecraft-esque voxel world? I found Minecraft's marvelous large worlds extremely slow to navigate, even with a quad core and meaty graphics card.  I assume Minecraft's slowness comes from:   Java, as spatial partitioning and memory management are faster in native C++. Weak world partitioning.   I could be wrong on both assumptions. However, this got me thinking about the best way to manage large voxel worlds. As it is a true 3D world, where a block can exist in any part of the world, it is basically a big 3D array [x][y][z], where each block in the world has a type (i.e BlockType.Empty = 0, BlockType.Dirt = 1, etc.)  I assume that to make this sort of world perform well, you would need to:   Use a tree of some variety (//) to split all the cubes out; it seems like an oct/kd would be the better option, as you can just partition on a per cube level not a per triangle level. Use some algorithm to work out which blocks can currently be seen, as blocks closer to the user could obfuscate the blocks behind, making it pointless to render them. Keep the block object themselves lightweight, so it is quick to add and remove them from the trees.   I guess there is no right answer to this, but I would be interested to see peoples' opinions on the subject.  How would you improve performance in a large voxel-based world? How to truncate all logfiles? can anybody give me a solution to truncate all logfile in /var/log/ directory?  and a question just for knowledge, is it a good idea or not?  #!/bin/bash LOGDIR="/var/log" for logfile in $(ls $LOGDIR/*log) do   truncate -s 0 $logfile done Show that $(l_1)^* \cong l_{\infty}$ Cardinality of the set of bijective functions on $\mathbb{N}$? Page number position I am working on a long document in LaTeX with documentclass book. I need the page number to always be in the upper right corner of each page, even if that page is the first page of a chapter (right now on 1st pages of chapters, the page number is bottom-centered, on all other pages it's top-right).  I control the position of the page number with fancyhdr:  \usepackage{fancyhdr} \pagestyle{fancy} \lhead{} \chead{} \rhead{\thepage} \lfoot{} \cfoot{} \rfoot{} \renewcommand{\headrulewidth}{0pt}   Also, I don't know if the problem is related but my chapters do not start from the top of the page. There is a white area, then comes chapter X, then a newline with the chapter line. What I also want is the chapter to start from the top of the page.  The main question here is how I can get the page number to always appear in the upper right corner, I mention the thing with the chapter title position only in case that might be related. Sum from $n=1$ to $N$ of $\sin(nx)/2^n$ The question states:    I'm not sure what to do here. I used the geometric sum to do $2^{-n}$, but I can't think of a way to sum $\sin(n\theta)$ to get the required RHS.    Further working     Apologies for maybe being slow or missing something obvious here... I don't know how to get it into required form. Layers with same coordinates not lining up I have a project where I have a few layers (State of Texas, cities, roads, etc.). They are all resaved and projected to NAD83 / UTM zone 14N EPSG: 26914. The project CRS is also NAD83 / UTM zone 14N EPSG: 26914 and on the fly projection is enabled. I added a text delimited file and cannot get them to line up. I checked the attribute table of the delimited file and the coordinates are correct. I cross-checked this with a point close to where a few of the points from the delimited file are and they are very close so in theory they should be lining up. I tried to save the delimited file and save it with the same projection and add the shp file back in and that did not work. Anyone have any ideas? I can't think of anything else to try. Real Analysis: Continuity of a Composition Function Suppose $f$ and $g$ are functions such that $g$ is continuous at $a$, and $f$ is continuous at $g(a)$. Show the composition $f(g(x))$ is continuous at $a$.  My idea: Can I go straight from definition and take $\delta=\min\{\delta_1,\delta_2\}$, where $\delta_1$ is used for the continuity of $g$ at $a$ and $\delta_2$ is used for f being continuous at $g(a)$. In my proof I just treat $g(a)$ as a point when referring to the composition. So it goes like this:  Proof: Given $\epsilon&gt;0$, take $\delta=\min\{\delta_1,\delta_2\}$. Then $0&lt;|x-g(a)|&lt;\delta$ which implies $|f(g(x))-f(g(a))|&lt;\epsilon$. I cannot boot to the desktop because I filled the file system. How do I reclaim some space? My memory is completely full when I tried following the data recovery and copied the wrong file using command line tool Test Disk. As it was taking so long to copy, I turned it off and I realized I copied the wrong file. Now my laptop memory is now full and lead me to more problems.  I have had similar problems to :       Now my screen keeps blinking:   Can anybody help? Many thanks. Wish you all the best. Show that AB is singular if A is singular Actually I need to show that $\det(AB) = \det(A)\det(B)$ if $A$ is a singular matrix.  The determinant of $A$ is $0$ if $A$ is singular, so $\det(AB)$ has to be $0$ as well, but I have problems showing that $AB$ is singular if $A$ is singular. How can I show that?