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• Find the "largest" dense sub matrix in a large sparse matrix

  - by BCS

  Given a large sparse matrix (say 10k+ by 1M+) I need to find a subset, not necessarily continuous, of the rows and columns that form a dense matrix (all non-zero elements). I want this sub matrix to be as large as possible (not the largest sum, but the largest number of elements) within some aspect ratio constraints. Are there any known exact or aproxamate solutions to this problem? A quick scan on Google seems to give a lot of close-but-not-exactly results. What terms should I be looking for? edit: Just to clarify; the sub matrix need not be continuous. In fact the row and column order is completely arbitrary so adjacency is completely irrelevant. A thought based on Chad Okere's idea Order the rows from largest count to smallest count (not necessary but might help perf) Select two rows that have a "large" overlap Add all other rows that won't reduce the overlap Record that set Add whatever row reduces the overlap by the least Repeat at #3 until the result gets to small Start over at #2 with a different starting pair Continue until you decide the result is good enough

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• How would you solve this graph theory handshake problem in python?

  - by Zachary Burt

  I graduated college last year with a degree in Psychology, but I also took a lot of math for fun. I recently got the book "Introductory Graph Theory" by Gary Chartrand to brush up on my math and have some fun. Here is an exercise from the book that I'm finding particularly befuddling: Suppose you and your husband attended a party with three other married couples. Several handshakes took place. No one shook hands with himself (or herself) or with his (or her) spouse, and no one shook hands with the same person more than once. After all the handshaking was completed, suppose you asked each person, including your husband, how many hands he or she had shaken. Each person gave a different answer. a) How many hands did you shake? b) How many hands did your husband shake? Now, I've been reasoning about this for a while, and trying to draw sample graphs that could illustrate a solution, but I'm coming up empty-handed. My logic is this: there are 8 different vertices in the graph, and 7 of them have different degrees. The values for the degrees must therefore be 0, 1, 2, 3, 4, 5, 6, and x. The # of degrees for one married couple is (0, 6). Since all graphs have an even number of odd vertices, x must be either 5, 3, or 1. What's your solution to this problem? And, if you could solve it in python, how would you do it? (python is fun.) Cheers.

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• How would you solve this graph theory handshake problem in python?

  - by Zachary Burt

  I graduated college last year with a degree in Psychology, but I also took a lot of math for fun. I recently got the book "Introductory Graph Theory" by Gary Chartrand to brush up on my math and have some fun. Here is an exercise from the book that I'm finding particularly befuddling: Suppose you and your husband attended a party with three other married couples. Several handshakes took place. No one shook hands with himself (or herself) or with his (or her) spouse, and no one shook hands with the same person more than once. After all the handshaking was completed, suppose you asked each person, including your husband, how many hands he or she had shaken. Each person gave a different answer. a) How many hands did you shake? b) How many hands did your husband shake? Now, I've been reasoning about this for a while, and trying to draw sample graphs that could illustrate a solution, but I'm coming up empty-handed. My logic is this: there are 8 different vertices in the graph, and 7 of them have different degrees. The values for the degrees must therefore be 0, 1, 2, 3, 4, 5, 6, and x. The # of degrees for one married couple is (0, 6). Since all graphs have an even number of odd vertices, x must be either 5, 3, or 1. What's your solution to this problem? And, if you could solve it in python, how would you do it? (python is fun.) Cheers.

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• removing white space in word

  - by nightcoder1

  how do i remove the white space from a msword document?

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• Getting java.lang.OutOfMemoryError: Java heap space

  - by user1371176

  I am getting an Exception in thread "HSQLDB Connection @3c50507" java.lang.OutOfMemoryError: Java heap space, when running a JSP. what is the thing that is out of memory? eclipse, HSQLDB or Tomcat?? i am using all that in a Mac OS X 10.7.4 When i start HSQLDB, then i get by console this exception: [Server@122ce908]: From command line, use [Ctrl]+[C] to abort abruptly Exception in thread "HSQLDB Connection @2e716cb7" java.lang.OutOfMemoryError: Java heap space at org.hsqldb.lib.HsqlByteArrayOutputStream.ensureRoom(Unknown Source) at org.hsqldb.rowio.RowOutputBinary.ensureRoom(Unknown Source) at org.hsqldb.lib.HsqlByteArrayOutputStream.write(Unknown Source) at org.hsqldb.rowio.RowOutputBinary.writeByteArray(Unknown Source) at org.hsqldb.rowio.RowOutputBinary.writeBinary(Unknown Source) at org.hsqldb.rowio.RowOutputBase.writeData(Unknown Source) at org.hsqldb.Result.write(Unknown Source) at org.hsqldb.Result.write(Unknown Source) at org.hsqldb.ServerConnection.run(Unknown Source) at java.lang.Thread.run(Thread.java:680) What does this all mean?

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• Python, dictionaries, and chi-square contingency table

  - by rohanbk

  I have a file which contains several lines in the following format (word, time that the word occurred in, and frequency of documents containing the given word within the given instance in time): #inputfile <word, time, frequency> apple, 1, 3 banana, 1, 2 apple, 2, 1 banana, 2, 4 orange, 3, 1 I have Python class below that I used to create 2-D dictionaries to store the above file using as the key, and frequency as the value: class Ddict(dict): ''' 2D dictionary class ''' def __init__(self, default=None): self.default = default def __getitem__(self, key): if not self.has_key(key): self[key] = self.default() return dict.__getitem__(self, key) wordtime=Ddict(dict) # Store each inputfile entry with a <word,time> key timeword=Ddict(dict) # Store each inputfile entry with a <time,word> key # Loop over every line of the inputfile for line in open('inputfile'): word,time,count=line.split(',') # If <word,time> already a key, increment count try: wordtime[word][time]+=count # Otherwise, create the key except KeyError: wordtime[word][time]=count # If <time,word> already a key, increment count try: timeword[time][word]+=count # Otherwise, create the key except KeyError: timeword[time][word]=count The question that I have pertains to calculating certain things while iterating over the entries in this 2D dictionary. For each word 'w' at each time 't', calculate: The number of documents with word 'w' within time 't'. (a) The number of documents without word 'w' within time 't'. (b) The number of documents with word 'w' outside time 't'. (c) The number of documents without word 'w' outside time 't'. (d) Each of the items above represents one of the cells of a chi-square contingency table for each word and time. Can all of these be calculated within a single loop or do they need to be done one at a time? Ideally, I would like the output to be what's below, where a,b,c,d are all the items calculated above: print "%s, %s, %s, %s" %(a,b,c,d)

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• translation/rotation of a HUD against a camera using vectors in Euclidian 3D space

  - by Jakob

  i've got 2 points in 3D space: the camera position and the camera lookAt. the camera movement is restricted akin to typical first person shooter games. you can move the cam freely, tilt horizontally and up to 90 degrees vertically, but not roll. so now i want to draw a HUD to the screen, on which i can move the mouse freely, with the position of the cursor correctly translating into 3D space. the easy part was to draw something directly in front of the camera. V0 = camPos; V1 = lookAt; V2 = lookAt-camPos; normalize V2; mutiply V2 according to camera frustum V3 = V0+V2 draw something at V3 now the part i don't get: i could use V3 and add to that the rotations of the cam combined with the x/y of the mouse cursor, somehow, right? that's what i want.

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• Multithreaded program in C: calculating thread stack space

  - by SlappyTheFish

  Situation: I am writing a program in C that maintains a number of threads. Once a thread ends, a new one is created. Each thread forks - the child runs a PHP process via exec() and the parent waits for it to finish. Each PHP process takes the next item from a queue, processes it and exits. Basic code: http://www.4pmp.com/2010/03/multitasking-php-in-parallel/ Problem: The PHP processes are Symfony tasks and Symfony requires a fairly huge amount of memory. How can I safely calculate the required stack space for each thread so that PHP processes will have enough memory? The memory limit set in php.ini is 128Mb so should I allocate this much space in the stack?

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• Space-based architecture?

  - by rcampbell

  One chapter in Pragmatic Programmer recommends looking at a blackboard/space-based architecture + a rules engine as a more flexible alternative to a traditional workflow system. The project I'm working on currently uses a workflow engine, but I'd like to evaluate alternatives. I really feel like a SBA would be a better solution to our business problems, but I'm worried about a total lack of community support/user base/venders/options. JavaSpaces is dead, and the JINI spin-off Apache River seems to be on life support. SemiSpace looks perfect, but it's a one-man show. The only viable solution seems to be GigaSpaces. I'd like to hear your thoughts on space based architecture and any experiences you've had with real world implementations.

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• Sorting Space Delimited Numbers with Linux/Bash

  - by syker

  Is there a Linux utility of a bash command I can use to sort a space delimited string of numbers?

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• Is it possible to implement bitwise operators using integer arithmetic?

  - by Statement

  Hello World! I am facing a rather peculiar problem. I am working on a compiler for an architecture that doesn't support bitwise operations. However, it handles signed 16 bit integer arithmetics and I was wondering if it would be possible to implement bitwise operations using only: Addition (c = a + b) Subtraction (c = a - b) Division (c = a / b) Multiplication (c = a * b) Modulus (c = a % b) Minimum (c = min(a, b)) Maximum (c = max(a, b)) Comparisons (c = (a < b), c = (a == b), c = (a <= b), et.c.) Jumps (goto, for, et.c.) The bitwise operations I want to be able to support are: Or (c = a | b) And (c = a & b) Xor (c = a ^ b) Left Shift (c = a << b) Right Shift (c = a b) (All integers are signed so this is a problem) Signed Shift (c = a b) One's Complement (a = ~b) (Already found a solution, see below) Normally the problem is the other way around; how to achieve arithmetic optimizations using bitwise hacks. However not in this case. Writable memory is very scarce on this architecture, hence the need for bitwise operations. The bitwise functions themselves should not use a lot of temporary variables. However, constant read-only data & instruction memory is abundant. A side note here also is that jumps and branches are not expensive and all data is readily cached. Jumps cost half the cycles as arithmetic (including load/store) instructions do. On other words, all of the above supported functions cost twice the cycles of a single jump. Some thoughts that might help: I figured out that you can do one's complement (negate bits) with the following code: // Bitwise one's complement b = ~a; // Arithmetic one's complement b = -1 - a; I also remember the old shift hack when dividing with a power of two so the bitwise shift can be expressed as: // Bitwise left shift b = a << 4; // Arithmetic left shift b = a * 16; // 2^4 = 16 // Signed right shift b = a >>> 4; // Arithmetic right shift b = a / 16; For the rest of the bitwise operations I am slightly clueless. I wish the architects of this architecture would have supplied bit-operations. I would also like to know if there is a fast/easy way of computing the power of two (for shift operations) without using a memory data table. A naive solution would be to jump into a field of multiplications: b = 1; switch (a) { case 15: b = b * 2; case 14: b = b * 2; // ... exploting fallthrough (instruction memory is magnitudes larger) case 2: b = b * 2; case 1: b = b * 2; } Or a Set & Jump approach: switch (a) { case 15: b = 32768; break; case 14: b = 16384; break; // ... exploiting the fact that a jump is faster than one additional mul // at the cost of doubling the instruction memory footprint. case 2: b = 4; break; case 1: b = 2; break; }

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• Android edittext prevent space in the field

  - by Faisal khan

  How can i prevent user to enter white space in the edit field ??

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• Rotation towards an object in 3d space

  - by retoucher

  hello, i have two coordinates on a 2d plane in 3d space, and am trying to rotate one coordinate (a vector) to face the other coordinate. my vertical axis is the y-axis, so if both of the coordinates are located flat on the 2d plane, they would both have a y-axis of 0, and their x and z coordinates determine their position length/width-wise on the plane. right now, i'm calculating the angle like so (language agnostic): angle = atan2(z2-z1,x2-x1); and am rotating/translating in space like so: pushMatrix(); rotateY(angle); popMatrix(); this doesn't seem to be working though. are my calculations/process correct?

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• count of distinct acyclic paths from A[a,b] to A[c,d]?

  - by Sorush Rabiee

  I'm writing a sokoban solver for fun and practice, it uses a simple algorithm (something like BFS with a bit of difference). now i want to estimate its running time ( O and omega). but need to know how to calculate count of acyclic paths from a vertex to another in a network. actually I want an expression that calculates count of valid paths, between two vertices of a m*n matrix of vertices. a valid path: visits each vertex 0 or one times. have no circuits for example this is a valid path: but this is not: What is needed is a method to find count of all acyclic paths between the two vertices a and b. comments on solving methods and tricks are welcomed.

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• LaTeX - vertical space equivalent of \makebox ?

  - by Rory

  I'm making a LaTeX document and I'm getting success with \makebox, which puts text in an invisible box and will add extra horizontal whitespace to the end to make the whole thing fit within the size you specify. Is there something like that for vertical space? I have a few variable length paragraphs, images, etc. that I want to put in this vertical box. I want LaTeX to put in the right amount of vertical space (at the bottom) so that the whole thing is of the set size that I give it.

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• Counting problem: possible sudoko tables?

  - by Sorush Rabiee

  Hi, I'm working on a sudoko solver. my method is using a game tree and explore possible permutations for each set of digits by DFS Algorithm. in order to analyzing problem, i want to know what is the count of possible valid and invalid sudoko tables? - a 9*9 table that have 9 one, 9 two, ... , 9 nine. (this isn't exact duplicate by this question) my solution is: 1- First select 9 cells for 1s: (*) 2- and like (1) for other digits (each time, 9 cells will be deleted from remaining available cells): C(81-9,9) , C(81-9*2,9) .... = 3- finally multiply the result by 9! (permutation of 123456789 in (*)) this is not equal to accepted answer of this question but problems are equivalent. what did i do wrong?

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• count of paths from A[a,b] to A[c,d] without duplicating?

  - by Sorush Rabiee

  I write a sokoban solver for fun and practice, it uses a simple algorithm (something like BFS). now i want to estimate its running time ( O and omega). but i need to know how to calculate count of paths from a vertex to another in a network. each path from a to b is a sequence of edges with no circuit. for example this is a correct path: http://www.imgplace.com/viewimg143/4789/501k.png but this is not: http://www.imgplace.com/viewimg143/6140/202.png

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• Line break and also getting space in HL7 message

  - by user1280098

  My BizTalk receive XML message as a input message. I am converting that message to HL7 message using Transform in orchestration. Now if input message consists of any empty field in any of the node, the HL7 message breaks up at that postion and also include space in that message. Can anyone help me to resolve this issue? following is my HL7 message: Note --- Copy this message in Textpad to get to know exact space in it MSH|^~\&|EEHR^bbbbbbbbbb|aaaaaaaaaaaaaaaaa^12699^DNS|KYIR|CDP|201103060733||VXU^V04|14962|P|2.3.1|||| PID|1||765874316^^^^SS||ssssss^anan^T|wwwww^^^^^^M|20100217|M||2135-2^YYYYYYYY or jjjjjj^HL70005|5896 hyhyhyhy Ave^Apt# 112^Wanta Fe^NM^85678^XXX^H^^049||5033331120X ^PRN^PH^^^505^5551120^~^NET^X.400^[email protected]|5056083515X4365^WPN^PH^^^505^6086715^4365|es^English^HL70296||||215486702|||H^erererer or qwqwqw^HL70189|bnbnbn|Y|1|||| Thanks.

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• finding ALL cycles in a huge sparse matrix

  - by Andy

  Hi there, First of all I'm quite a Java beginner, so I'm not sure if this is even possible! Basically I have a huge (3+million) data source of relational data (i.e. A is friends with B+C+D, B is friends with D+G+Z (but not A - i.e. unmutual) etc.) and I want to find every cycle within this (not necessarily connected) directed graph. I've found this thread (http://stackoverflow.com/questions/546655/finding-all-cycles-in-graph/549402#549402) which has pointed me to Donald Johnson's (elementary) cycle-finding algorithm which, superficially at least, looks like it'll do what I'm after (I'm going to try when I'm back at work on Tuesday - thought it wouldn't hurt to ask in the meanwhile!). I had a quick scan through the code of the Java implementation of Johnson's algorithm (in that thread) and it looks like a matrix of relations is the first step, so I guess my questions are: a) Is Java capable of handling a 3+million*3+million matrix? (was planning on representing A-friends-with-B by a binary sparse matrix) b) Do I need to find every connected subgraph as my first problem, or will cycle-finding algorithms handle disjoint data? c) Is this actually an appropriate solution for the problem? My understanding of "elementary" cycles is that in the graph below, rather than picking out A-B-C-D-E-F it'll pick out A-B-F, B-C-D etc. but that's not the end of the world given the task. E / \ D---F / \ / \ C---B---A d) If necessary, I can simplify the problem by enforcing mutuality in relations - i.e. A-friends-with-B <== B-friends-with-A, and if really necessary I can maybe cut down the data size, but realistically it is always going to be around the 1mil mark. z) Is this a P or NP task?! Am I biting off more than I can chew? Thanks all, any help appreciated! Andy

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• Trying to test space in filesystem on Unix

  - by Buzkie

  I need to check if I Filesystem exists, and if it does exist there is 300 MB of space in it. What I have so far: if [ "$(df -m /opt/IBM | grep -vE '^Filesystem' | awk '{print ($3)}')" < "300" ] then echo "not enough space in the target filesystem" exit 1 fi This throws an error. I don't really know what I'm doing in shell. My highest priority is AIX but I'm trying to get it to work for HP and Sun too. Please help. -Alex

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• SQL Server 2008, not enough disk space

  - by snorlaks

  Hello, I'm executing sql query on my database. I have SQL Server 2008 installed on my D harddrive which has 55 GB free space. I have also C drive which has sth like 150 MB free (right now). While executing that query on quite a big table (16 GB) I have an error: An error occurred while executing batch. Error message is: Not enough disk space. I would like to know if there is any possibility that I can make SQL Server to use D drive instead of C Or maybe there is any other problem with what I'm doing ? Thanks for help

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• Avoid copying of data between user and kernel space and vice-versa

  - by bala1486

  Hello, I am developing a active messaging protocol for parallel computation that replaces TCP/IP. My goal is to decrease the latency of a packet. Since the environment is a LAN, i can replace TCP/IP with simpler protocol to reduce the packet latency. I am not writing any device driver and i am just trying to replace the TCP/IP stack with something simpler. Now I wanted to avoid copying of a packet's data from user space to kernel space and vice-versa. I heard of the mmap(). Is it the best way to do this? If yes, it will be nice if you can give links to some examples. I am a linux newbie and i really appreciate your help.. Thank you... Thanks, Bala

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• .htaccess URL is being cut at a space (I'm using Codeigniter)

  - by Ice

  I've used the following code to map https://live.example.com on to http://example.com/api Options +FollowSymLinks RewriteEngine On RewriteCond %{HTTPS} =on RewriteCond %{HTTP_HOST} ^live\.example\.com [NC] RewriteRule (.+)$ "http://example.com/api/$1" [L,P] The following url: https://live.example.com/userlinks/xml/John%20James/MvPjeUTo15/ Is suppose to map onto: http://example.com/api/userlinks/xml/John%20James/MvPjeUTo15/ Instead it maps it to: http://example.com/api/userlinks/xml/John So it seems to cut it at the space. I am using the Codeigniter framework but I am not sure if the problem lies there. Also using %20 or just a space in the url bar produces no different results. Anyone any idea and/or solution why this happens? Thank you very much, Ice

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• blank space on google home page

  - by topgun_ivard

  2 questions, i was doing nothing productive, and tried selecting the google home page (a left click drag and select whole page) on google.com i see that beside the search box, on the left side, there is an empty space &nbsp; i looked up the source code and there indeed was a <td width=25%>&nbsp;</td> stupid as it may sound, but i was still curious to know why the blank space is out there..or is it just a simple typo?? :) also, any idea what window.lol&&lol() does? curious yet again, google search didnt get me any result and i thought i would turn to stackoverflow to enlighten me... thanks, ivar

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• How can you transform a set of numbers into mostly whole ones?

  - by Alice

  Small amount of background: I am working on a converter that bridges between a map maker (Tiled) that outputs in XML, and an engine (Angel2D) that inputs lua tables. Most of this is straight forward However, Tiled outputs in pixel offsets (integers of absolute values), while Angel2D inputs OpenGL units (floats of relative values); a conversion factor between these two is needed (for example, 32px = 1gu). Since OpenGL units are abstract, and the camera can zoom in or out if the objects are too small or big, the actual conversion factor isn't important; I could use a random number, and the user would merely have to zoom in or out. But it would be best if the conversion factor was selected such that most numbers outputted were small and whole (or fractions of small whole numbers), because that makes it easier to work with (and the whole point of the OpenGL units is that they are easy to work with). How would I find such a conversion factor reliably? My first attempt was to use the smallest number given; this resulted in no fractions below 1, but often lead to lots of decimal places where the factors didn't line up. Then I tried the mode of the sequence, which lead to the largest number of 1's possible, but often lead to very long floats for background images. My current approach gets the GCD of the whole sequence, which, when it works, works great, but can easily be thrown off course by a single bad apple. Note that while I could easily just pass the numbers I am given along, or pick some fixed factor, or use one of the conversions I specified above, I am looking for a method to reliably scale this list of integers to small, whole numbers or simple fractions, because this would most likely be unsurprising to the end user; this is not a one off conversion. The end users tend to use 1.0 as their "base" for manipulations (because it's simple and obvious), so it would make more sense for the sizes of entities to cluster around this.

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