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• Problem with graphiz on Unix

  - by J3n

  When I'm on Unix, my graphs with graphphiz are less nice. The tail or the head of the edge is not always linked to the boundary of the port. You can see the result here : http://www.freeimagehosting.net/image.php?59d8eb4b30.jpg <xsl:value-of select="$source"/>:<xsl:value-of select="$prot"/> -&gt; <xsl:value-of select="$destination"/>:<xsl:value-of select="$prot"/>[color="black",label="<xsl:value-of select="$prot"/>",fontcolor="black",tailclip=true,headclip=true];

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• What is it about Fibonacci numbers?

  - by Ian Bishop

  Fibonacci numbers have become a popular introduction to recursion for Computer Science students and there's a strong argument that they persist within nature. For these reasons, many of us are familiar with them. They also exist within Computer Science elsewhere too; in surprisingly efficient data structures and algorithms based upon the sequence. There are two main examples that come to mind: Fibonacci heaps which have better amortized running time than binomial heaps. Fibonacci search which shares O(log N) running time with binary search on an ordered array. Is there some special property of these numbers that gives them an advantage over other numerical sequences? Is it a density quality? What other possible applications could they have? It seems strange to me as there are many natural number sequences that occur in other recursive problems, but I've never seen a Catalan heap.

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• What, if any, is wrong with this definition of letrec in Scheme?

  - by Lajla

  R5RS gives proposed macro definitions for library forms of syntax: http://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-10.html#%_sec_7.3 Which also defines letrec, in a very complicated way, certainly not how I would define it, I would simply use: (define-syntax letrec2 (syntax-rules () ((letrec2 ((name val) ...) body bodies ...) ((lambda () (define name val) ... body bodies ...))))) As far as I understand the semantics of letrec, which I use very often as a named let. It works in this way, however as I've had my fair share of debates with philosophers who think they can just disprove special relativity or established phonological theories, I know that when you think you have a simple solution to a complex problem, it's probably WRONG. There has got to be some point where this macro does not satify the semantics of letrec else they'd probably have used it. In this definition, the definitions are local to the body of the letrec, they can refer to each other for mutual recursion, I'm not quite sure what (if any) is wrong.

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• generate all subsets of size k from a set

  - by Kumar

  hi, i want to generate all the subsets of size k from a set. eg:-say i have a set of 6 elements, i have to list all the subsets in which the cardinality of elements is 3. I tried looking for solution,but those are code snippets. Its been long since I have done coding,so I find it hard to understand the code and construct a executable program around it. A complete executable program in C or C++ will be quite helpful. Hoping of an optimal solution using recursion. Thanks in advance. Kumar.

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• Find directories not containing a specific directory

  - by Morgan ARR Allen

  Been searching around for a bit and cannot find a solution for this one. I guess I'm looking for a leaf-directory by name. In this example I'd like to get a list of directories call 'modules' that do NOT have a subdirectory called module. modules/package1/modules/spackage1 modules/package1/modules/spackage2 modules/package1/modules/spackage3/modules modules/package1/modules/spackage3/modules/spackage1 modules/package2/modules/ The list I desire would contain modules/package1/modules/spackage3/modules/ modules/package2/modules/ All the directories named module that do not have a subdirectory called module I started with trying something this with no luck find . -name modules \! -exec sh -c 'find -name modules' \; -exec works on exit code, okay lets pass the count as exit code find . -name modules -exec sh -c 'exit $(find {} -name modules|grep -n ""|tail -n1|cut -d: -f1)' \; This should take the count of each subdirectory called modules and exit with it. No such love.

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• Monitoring .NET ASP.NET Applications

  - by James Hollingworth

  I have a number of applications running on top of ASP.NET I want to monitor. The main things I care about are: Exceptions: We currently some custom code which will email us when an exception occurs. If the application is failing hard it will crash our outlook... I know (and use) elmah which partly solves the problem however it is still just a big table of exceptions with a pretty(ish) UI. I want something that makes sense of all of these exceptions (e.g. groups exceptions, alerts when new ones occur, tells me what the common ones are that I should fix, etc) Logging: We currently log to files which are then accessible via a shared folder which dev's grep & tail. Does anyone know of better ways of presenting this information. In an ideal world I want to associate it with exceptions. Performance: Request times, memory usage, cpu, etc. whatever stats I can get I'm guessing this is probably going to be solved by a number of tools, has anyone got any suggestions?

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• F# script to application

  - by sudaly

  I have written two small scripts, First one maintains a dictionary of current stock prices for a set of securities. I am using recursion to listen to a named pipe. Whenever there is something available on the name pipe, it updates the security price and goes right back and start listening to the pipe. The second one periodically reads the stock price of some security from the price cache of the first program and performs come calculation. But I have no idea how to make these two programs communicate. I somehow need to make my second programs start the first program and let it run in the background and get the price whenever it needs it. Can someone point me in the right direction? Thank you, -Niran

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• Find the min max and average of one column of data in python

  - by user1440194

  I have a set of data that looks like this 201206040210 -3461.00000000 -8134.00000000 -4514.00000000 -4394.00000000 0 201206040211 -3580.00000000 -7967.00000000 -4614.00000000 -7876.00000000 0 201206040212 -3031.00000000 -9989.00000000 -9989.00000000 -3419.00000000 0 201206040213 -1199.00000000 -6961.00000000 -3798.00000000 -5822.00000000 0 201206040214 -2940.00000000 -5524.00000000 -5492.00000000 -3394.00000000 0 I want to take the second to last column and find the min, max, and average. Im a little confused on how to use split when the columns are delimited by a space and -. i Figure once i do that i can use min() and max function. I have written a shell script to do the same here #!/bin/ksh awk '{print substr($5,2);}' data' > /data1 sort -n data1 > data2 tail -1 data2 head -1 data2 awk '{sum+=$1} END {print "average = ",sum/NR}' data2 Im just not sure how to do this in python. Thanks

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• Rearrange a python list into n lists, by column

  - by Ben R

  Trying to solve this at this hour has gotten my mind into a tail-spin: I want to rearrange a list l into a list of n lists, where n is the number of columns. e.g., l = [1,2,3,4,5,6,7,8] n = 5 ==> [[1,6][2,7][3,8][4][5]] another example: l = [1,2,3,4,5,6,7,8,9,10] n = 4 ==> [[1,5,9],[2,6,10],[3,7][4,8] Can someone please help me out with an algorithm? Feel free to use any python awesomeness that's available; I'm sure theres some cool mechanism that's a good fit for this, i just can't think of it.

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• Efficient bitshifting an array of int?

  - by nn

  Hi, To be on the same page, let's assume sizeof(int)=4 and sizeof(long)=8. Given an array of integers, what would be an efficient method to bitshift the array to either the left or right? I am contemplating an auxiliary variable such as a long, that will compute the bitshift for the first pair of elements (index 0 and 1) and set the first element (0). Continuing in this fashion the bitshift for elements (index 1 and 2) will be computer, and then index 1 will be set. I think this is actually a fairly efficient method, but there are drawbacks. I cannot bitshift greater than 32 bits. I think using multiple auxiliary variables would work, but I'm envisioning recursion somewhere along the line.

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• Enumerating all hamiltonian paths from start to end vertex in grid graph

  - by Eric

  Hello, I'm trying to count the number of Hamiltonian paths from a specified start vertex that end at another specified vertex in a grid graph. Right now I have a solution that uses backtracking recursion but is incredibly slow in practice (e.g. O(n!) / 3 hours for 7x7). I've tried a couple of speedup techniques such as maintaining a list of reachable nodes, making sure the end node is still reachable, and checking for isolated nodes, but all of these slowed my solution down. I know that the problem is NP-complete, but it seems like some reasonable speedups should be achievable in the grid structure. Since I'm trying to count all the paths, I'm sure that the search must be exhaustive, but I'm having trouble figuring out how to prune out paths that aren't promising. Does anyone have some suggestions for speeding the search up? Or an alternate search algorithm?

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• Pattern matching for lambda expressions

  - by alphomega

  21 --Primitive recursion constructor 22 pr :: ([Int] -> Int) -> ([Int] -> Int) -> ([Int] -> Int) 23 pr f g = \xs 0 -> f xs 24 pr f g = \xs (y+1) -> g xs y ((pr f g) xs y) I want the function this function creates to act differently on different inputs, so that it can create a recursive function. As expected, the above code doesn't work. How do I do something like pattern matching, but for the function it creates? Thanks

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• Escaping Problem in bash using isql

  - by latz

  Hi there, I am currently working on a little backup script from some firebird databases and I've come up with a weird escaping problem that I don't seem to be able to solve. Here's the thing in my script I create a variable called sqllog in which I would like to put the output of a chain of commands, here it is. sqllog=echo "SELECT * FROM RDB\$DATABASE;" | isql -u SYSDBA -pass mypasswd localhost:mydatabase | tail -n 2 | head -n 1 | wc -l if I try to execute this in shell I get the following error Statement failed, SQLCODE = -204 Dynamic SQL Error -SQL error code = -204 -Table unknown -RDB -At line 1, column 15. Table unknown RDB means it didn't take my try to escape the $. thx for any help :)

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• Which is the best Linux C/C++ debugger (or front-end to gdb) to help teaching programming?

  - by omer.gimenez

  I teach a sort of "lite" C++ programming course to novices ("lite" meaning no pointers, no classes, just plain old C, plus references and STL string and vectors). Students have no previous experience in programming, so I believe that using an interactive debugger would help them understand program flow, variables, and recursion. The course is taught in Linux. Teaching them to use gdb is just overkill (they will not use nor understand most features). I just need something simple but easy to use: to see at which line the program is now, what is in the stack (local variables, previous calls, etc.). I look something similar to old Turbo Pascal or Turbo C++ Borland's debugger, or Visual Studio debugger. Thank you,

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• Implementing a recursive menu system a'la Joomla in CodeIgniter

  - by pettersolberg

  Hi I have some sites powered by Joomla, but with my current assignment I wanted to try something new and created with CodeIgniter a really basic CMS (just to suit my client's needs). Everything works fine except menus - multilevel menus like in Joomla, Drupal etc. with items and subitems... My question is: do you know of any tutorials or texts abut implementing such a structure. I've tried the recursion thinggy with while getting children's IDs move downwards from the parent while searching for the currently displayed item's ID. I've tried also the Drupalish way with having a path parameter enclosing ID's all the way from top to bottom '1/23/123/3'. But all in all it was just too chaotic - code something, try it out. If you have some idea on this topic - thanks in advice.

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• Another Permutation Word Conundrum... With Linq?

  - by CraigF

  I have seen many examples of getting all permutations of a given set of letters. Recursion seems to work well to get all possible combinations of a set of letters (though it doesn't seem to take into account if 2 of the letters are the same). What I would like to figure out is, could you use linq (or not) to get all possible combinations of letters down to 3 letter combinations. For example, given the letters: P I G G Y I want an array of all possible cominations of these letters so I can check against a word list (scrabble?) and eventually get a list of all possible words that you can make using those letters (from 3 letters up to the total, in this case 5 letters).

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• 'Recursive' LINQ calls

  - by Sir Psycho

  Hi, I'm trying to build an XML tree of some data with a parent child relationship, but in the same table. The two fields of importance are CompetitionID ParentCompetitionID Some data might be CompetitionID=1, ParentCompetitionID=null CompetitionID=2, ParentCompetitionID=1 CompetitionID=3, ParentCompetitionID=1 The broken query I have simply displays results in a flat format. Seeing that I'm working with XML, some sort of recursive functionality is required. I can do this using recursion, but would like to see the linq version. Any help appreciated. var results = from c1 in comps select new { c.CompetitionID, SubComps= from sc in comps.Where (c2 => c2.CompetitionID == c1.CompetitionID) select sc };

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• Write the longest possible loop.

  - by Abhay

  Hello Group, Recently I was asked this question in a technical discussion. What is the longest possible loop that can be written in a programming language? This loop has to be as long as possible and yet not an infinite loop and should not end-up crashing the program (Recursion etc...) I honestly did not know how to attack this problem, so I asked him if is it practically possible. He said using some computer science concepts, you can arrive at a hypothetical number which may not be practical but nevertheless it will still not be infinite. Anyone here; knows how to analyse / attack this problem. P.S. Choosing some highest limit for a type that can store the highest numerical value is apparently not an answer. Thanks in advance,

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• Binding in ContentControl Crash

  - by ImJames

  Can anyone tell me why this crashes my app? There seems to be some endless recursion by I can't figure out why. I get this exception Logical tree depth exceeded while traversing the tree. This could indicate a cycle in the tree <ContentControl Content="{Binding}"> <ContentControl.ContentTemplate> <DataTemplate> <Button Content="{Binding MyString}"/> </DataTemplate> </ContentControl.ContentTemplate> </ContentControl> And this is all I have as Source public MainWindow() { InitializeComponent(); MyString = "Test"; this.DataContext = this; } public string MyString { get; set; }

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• How to hash and check for equality of objects with circular references

  - by mfya

  I have a cyclic graph-like structure that is represented by Node objects. A Node is either a scalar value (leaf) or a list of n=1 Nodes (inner node). Because of the possible circular references, I cannot simply use a recursive HashCode() function, that combines the HashCode() of all child nodes: It would end up in an infinite recursion. While the HashCode() part seems at least to be doable by flagging and ignoring already visited nodes, I'm having some troubles to think of a working and efficient algorithm for Equals(). To my surprise I did not find any useful information about this, but I'm sure many smart people have thought about good ways to solve these problems...right? Example (python): A = [ 1, 2, None ]; A[2] = A B = [ 1, 2, None ]; B[2] = B A is equal to B, because it represents exactly the same graph. BTW. This question is not targeted to any specific language, but implementing hashCode() and equals() for the described Node object in Java would be a good practical example.

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• Problem with a recursive function to find sqrt of a number

  - by Eternal Learner

  Below is a simple program which computes sqrt of a number using Bisection. While executing this with a call like sqrtr(4,1,4) in goes into an endless recursion . I am unable to figure out why this is happening. Below is the function : double sqrtr(double N , double Low ,double High ) { double value = 0.00; double mid = (Low + High + 1)/2; if(Low == High) { value = High; } else if (N < mid * mid ) { value = sqrtr(N,Low,mid-1) ; } else if(N >= mid * mid) { value = sqrtr(N,mid,High) ; } return value; }

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• Finding the index of a given value in a pre-sorted array

  - by bobo

  Today, I went for an interview and the interviewer asked me how I would find the index of a given value (number) in a pre-sorted array like this: $preSortedArr=array(23,32,36,41,45,54); He also said that using recursion is not allowed. I think the function should look like this: function findIndexByValue($preSortedArray,$value){ //some codes here } What solution do you think he was expecting from me? EDIT: sorry, I forgot to add that, he originally asked me to write psuedo codes but I said I don't know. I tried to write in PHP, but I think he's expecting a language-independent solution.

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• how to exit recursive math formula and still get an answer

  - by calccrypto

  i wrote this python code, which from wolfram alpha says that its supposed to return the factorial of any positive value (i probably messed up somewhere), integer or not: from math import * def double_factorial(n): if int(n) == n: n = int(n) if [0,1].__contains__(n): return 1 a = (n&1) + 2 b = 1 while a<=n: b*=a a+= 2 return float(b) else: return factorials(n/2) * 2**(n/2) *(pi/2)**(.25 *(-1+cos(n * pi))) def factorials(n): return pi**(.5 * sin(n*pi)**2) * 2**(-n + .25 * (-1 + cos(2*n*pi))) * double_factorial(2*n) the problem is , say i input pi to 6 decimal places. 2*n will not become a float with 0 as its decimals any time soon, so the equation turns out to be pi**(.5 * sin(n*pi)**2) * 2**(-n + .25 * (-1 + cos(2*n*pi))) * double_factorial(loop(loop(loop(...))))) how would i stop the recursion and still get the answer? ive had suggestions to add an index to the definitions or something, but the problem is, if the code stops when it reaches an index, there is still no answer to put back into the previous "nests" or whatever you call them

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• Validates presence of each other in two associated models

  - by Sergey Alekseev

  I have the following two models: class Parent < ActiveRecord::Base has_one :child, dependent: :destroy validates :child, presence: true end class Child < ActiveRecord::Base belongs_to :parent validates :parent, presence: true end I want to create Parent object. If I do the following: Parent.create! or Factory(:parent) Exception raises: ActiveRecord::RecordInvalid: Validation failed: Child can't be blank But I can't create Child object without Parent object for the same reason - I need to create Parent object first in order to pass presence validation. As it appears I have some kind of infinite recursion here. How to solve it?

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• Show a django relationship in a template

  - by kevin_82

  I have a django model as follows: class Person(models.Model): name = models.CharField(max_length=255) class Relationship(models.Model): parent = models.ForeignKey(Person) child = models.ForeignKey(Person) description = models.TextField(blank=True) In my view, I pass a certain person, and the relationships in which he/she is parent: person = Person.objects.filter(name ='some name') descendant_relationships = Relationship.objects.filter(parent = person) An I want to show this person's descendants in a list in a template: <ul> {% for item in descendant_relationships%} <li> {{item.child.name}} - {{item.description}} </li> {% endfor %} </ul> But this template code will not show the children of children (i.e. grandchildren, great-grandchildren etc.). How can I get these lower level descendants to show up? I imagine recursion is necessary somewhere, but where?

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