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• Ubuntu 13.04 installation issues: unable to handle kernel paging request error

  - by user173944

  I wish I could say that I’ve done more for the Linux community as of recent but I am very VERY new to all of this and I feel very much in over my head. I figured I would install Ubuntu. on my computer and then I would learn and contribute to the community simultaneously. I will try to be as detailed as I can, please ask questions if you need clarification. I installed Ubuntu. 13.04 (64-bit) on my dell Inspiron 1501. This has an AMD Turion 64-bit TL-56 1.8 Ghz mobile processor. It is a dual core. It has an ATI Radeon Xpress 1150 chipset in it as well. As of right now I only have a total of 2Ghz ram, however I was planning on upgrading that in the near future so I opted for the 64-bit Ubuntu. 13.04. I first tried the live CD and everything seemed to be functioning correctly other than the wireless (but that's not the issue at hand, there are plenty of guides on the internet on how to get that functioning). The internet worked just fine when it was plugged in so no issues there. However, once I went from that to installing 13.04 (just 13.04, no dual partitioning... I want this computer to run strictly Ubuntu.) it did not work. It took me into a shell that I could not type anything into. In this shell it said Bug: unable to handle kernel paging and then it called a bunch of traces and froze up. I had to hard reset the laptop. I tried the boot-repair program multiple times with many different settings and typically after starting up the laptop would say something along the lines of recursive errors. will attempt to fix and then it would attempt to fix a couple of things, and then the computer would freeze up after the text said end trace... so I had to hard reset it again. I'm not an impatient person either, when I say it would freeze up it would be for a period of at least 15 minutes each time before I decided to hard reset. I attempted to install 12.10 on it instead and I got the same exact message, and when I ran boot-repair it did the same exact thing as before. I am currently in the process of running memtest64+ on the computer's memory, though I really don't believe that, nor any of the hardware is at fault due to the fact that it was still running windows vista perfectly when I had decided to switch over to Ubuntu. so far the memtest has came back just fine without any errors, but I’ve only been running it for approximately an hour. So this is the situation I’m in. I did notice when I was using the live disk that the video driver needed updated so I performed that, though I’m fairly certain that has nothing to do with this. I have also attempted (though I’m not certain that my attempt was successful in accomplishing what I had planned) to manually edit the grub settings by making acpi=0 along top of adding nomodeset to the boot commands. Like I said, I’m not sure I did that correctly though, but I’m fairly certain I did. If anyone needs any more information I will be more than happy to provide it, I will post back once I get the full results of the memtest. I very much appreciate any ideas anyone else has, I’ve been at this for a few days to no avail... thank you

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• How to use correctly the comments in C/++

  - by Lucio

  I'm learning to program in C and in my stage, the best form to use correctly the comments is writing good comments from the beginning. As the comments are not just for that one understands better the code but others too, I want to know the views of all of you to reach a consensus. So what I want is that the most experienced users edit the following code as you please. (If it's unnecessary, delete it; If it's wrong, correct it; If needed, add more) Thus there'll be multiple answers with different syntax and the responses with the most votes will be taken as referring when commenting. The code to copy, paste and edit to your pleasure is: (And I remark again, just import the comments, not the code) /* This programs find 1 number in 1 file. The file is binary type and has integers in series. The number is integer type and it's entered from the keyboard. When finished the program, a poster will show the results: Saying if the number is in the file or not. */ #include <stdio.h> //FUNCTION 1 //Open file 'path' and closes it. void openf(char path[]) { int num; //Read from Keyboard a Number and it save it into 'num' var printf("Ready for read number.\n\nNumber --> "); fflush(stdin); scanf("%d",&num); //Open file 'path' in READ mode FILE *fvar; fvar=fopen(path,"rb"); //IF error happens when open file, exit of function if (fvar==NULL) { printf("ERROR while open file %s in read mode.",path); exit(1); } /*Verify the result of 'funct' function IF TRUE, 'num' it's in the file*/ if (funct(path,fvar,num)) printf("The number %d it is in the file %s.",num,path); else printf("The number %d it is not in the file %s.",num,path); fclose(fvar); } /*FUNCTION 2 It is a recursive function. Reads number by number until the file is empty or the number is found. Parameters received: 'path' -> Directory file 'fvar' -> Pointer file 'num' -> Number to compare */ int funct(char path[],FILE *fvar,int num) { int compare; //FALSE condition when the pointer reaches the end if (fread(&compare,sizeof(int),1,fvar)>0) /*TRUE condition when the number readed is iqual that 'num' ELSE will go to the function itself*/ if (compare!=num) funct(path,fvar,num); else return 1; else return 0; } int main(int argc, char **argv) { char path[30]="file.bin"; //Direction of the file to process openf(path); //Function with algorithm return 0; }

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• Investigating Strategies For Functional Decomposition

  - by Liam McLennan

  Introducing Functional Decomposition Before I begin I must apologise. I think I am using the term ‘functional decomposition’ loosely, and probably incorrectly. For the purpose of this article I use functional decomposition to mean the recursive splitting of a large problem into increasingly smaller ones, so that the one large problem may be solved by solving a set of smaller problems. The justification for functional decomposition is that the decomposed problem is more easily solved. As software developers we recognise that the smaller pieces are more easily tested, since they do less and are more cohesive. Functional decomposition is important to all scientific pursuits. Once we understand natural selection we can start to look for humanities ancestral species, once we understand the big bang we can trace our expanding universe back to its origin. Isaac Newton acknowledged the compositional nature of his scientific achievements: If I have seen further than others, it is by standing upon the shoulders of giants   The Two Strategies For Functional Decomposition of Computer Programs Private Methods When I was working on my undergraduate degree I was taught to functionally decompose problems by using private methods. Consider the problem of painting a house. The obvious solution is to solve the problem as a single unit: public void PaintAHouse() { // all the things required to paint a house ... } We decompose the problem by breaking it into parts: public void PaintAHouse() { PaintUndercoat(); PaintTopcoat(); } private void PaintUndercoat() { // everything required to paint the undercoat } private void PaintTopcoat() { // everything required to paint the topcoat } The problem can be recursively decomposed until a sufficiently granular level of detail is reached: public void PaintAHouse() { PaintUndercoat(); PaintTopcoat(); } private void PaintUndercoat() { prepareSurface(); fetchUndercoat(); paintUndercoat(); } private void PaintTopcoat() { fetchPaint(); paintTopcoat(); } According to Wikipedia, at least one computer programmer has referred to this process as “the art of subroutining”. The practical issues that I have encountered when using private methods for decomposition are: To preserve the top level API all of the steps must be private. This means that they can’t easily be tested. The private methods often have little cohesion except that they form part of the same solution. Decomposing to Classes The alternative is to decompose large problems into multiple classes, effectively using a class instead of each private method. The API delegates to related classes, so the API is not polluted by the sub-steps of the problem, and the steps can be easily tested because they are each in their own highly cohesive class. Additionally, I think that this technique facilitates better adherence to the Single Responsibility Principle, since each class can be decomposed until it has precisely one responsibility. Revisiting my previous example using class composition: public class HousePainter { private undercoatPainter = new UndercoatPainter(); private topcoatPainter = new TopcoatPainter(); public void PaintAHouse() { undercoatPainter.Paint(); topcoatPainter.Paint(); } } Summary When decomposing a problem there is more than one way to represent the sub-problems. Using private methods keeps the logic in one place and prevents a proliferation of classes (thereby following the four rules of simple design) but the class decomposition is more easily testable and more compatible with the Single Responsibility Principle.

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• Class design issue

  - by user2865206

  I'm new to OOP and a lot of times I become stumped in situations similar to this example: Task: Generate an XML document that contains information about a person. Assume the information is readily available in a database. Here is an example of the structure: <Person> <Name>John Doe</Name> <Age>21</Age> <Address> <Street>100 Main St.</Street> <City>Sylvania</City> <State>OH</State> </Address> <Relatives> <Parents> <Mother> <Name>Jane Doe</Name> </Mother> <Father> <Name>John Doe Sr.</Name> </Father> </Parents> <Siblings> <Brother> <Name>Jeff Doe</Name> </Brother> <Brother> <Name>Steven Doe</Name> </Brother> </Siblings> </Relatives> </Person> Ok lets create a class for each tag (ie: Person, Name, Age, Address) Lets assume each class is only responsible for itself and the elements directly contained Each class will know (have defined by default) the classes that are directly contained within them Each class will have a process() function that will add itself and its childeren to the XML document we are creating When a child is drawn, as in the previous line, we will have them call process() as well Now we are in a recursive loop where each object draws their childeren until all are drawn But what if only some of the tags need to be drawn, and the rest are optional? Some are optional based on if the data exists (if we have it, we must draw it), and some are optional based on the preferences of the user generating the document How do we make sure each object has the data it needs to draw itself and it's childeren? We can pass down a massive array through every object, but that seems shitty doesnt it? We could have each object query the database for it, but thats a lot of queries, and how does it know what it's query is? What if we want to get rid of a tag later? There is no way to reference them. I've been thinking about this for 20 hours now. I feel like I am misunderstanding a design principle or am just approaching this all wrong. How would you go about programming something like this? I suppose this problem could apply to any senario where there are classes that create other classes, but the classes created need information to run. How do I get the information to them in a way that doesn't seem fucky? Thanks for all of your time, this has been kicking my ass.

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• Support for nested model and class validation with ASP.NET MVC 2.0

  - by Diep-Vriezer

  I'm trying to validate a model containing other objects with validation rules using the System.ComponentModel.DataAnnotations attributes was hoping the default MVC implementation would suffice: var obj = js.Deserialize(json, objectInfo.ObjectType); if(!TryValidateModel(obj)) { // Handle failed model validation. } The object is composed of primitive types but also contains other classes which also use DataAnnotications. Like so: public class Entry { [Required] public Person Subscriber { get; set; } [Required] public String Company { get; set; } } public class Person { public String FirstName { get; set;} [Required] public String Surname { get; set; } } The problem is that the ASP.NET MVC validation only goes down 1 level and only evaluates the properties of the top level class, as can be read on digitallycreated.net/Blog/54/deep-inside-asp.net-mvc-2-model-metadata-and-validation. Does anyone know an elegant solution to this? I've tried xVal, but they seem to use a non-recursive pattern (http://blog.stevensanderson.com/2009/01/10/xval-a-validation-framework-for-aspnet-mvc/). Someone must have run into this problem before right? Nesting objects in your model doesn't seem so weird if you're designing a web service.

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• What's the "best" database for embedded?

  - by mawg

  I'm an embedded guy, not a database guy. I've been asked to redesign an existing system which has bottlenecks in several places. The embedded device is based around an ARM 9 processor running at 220mHz. There should be a database of 50k entries (may increase to 250k) each with 1k of data (max 8 filed). That's approximate - I can try to get more precise figures if necessary. They are currently using SqlLite 2 and planning to move to SqlLite 3. Without starting a flame war - I am a complete d/b newbie just seeking advice - is that the "best" decision? I realize that this might be a "how long is a piece of string?" question, but any pointers woudl be greatly welcomed. I don't mind doing a lot of reading & research, but just hoped that you could get me off to a flying start. Thanks. p.s Again, a total rewrite, might not even stick with embedded Linux, but switch to eCos, don't worry too much about one time conversion between d/b formats. Oh, and accesses should be infrequent, at most one every few seconds. edit: ok, it seems they have 30k entries (may reach 100k or more) of only 5 or 6 fields each, but at least 3 of them can be a search key for a record. They are toying with "having no d/b at all, since the data are so simple", but it seems to me that with multiple keys, we couldn't use fancy stuff like a quicksort() type search (recursive, binary search). Any thoughts on "no d/b", just data-structures? Btw, one key is 800k - not sure how well SqlLite handles that (maybe with "no d/b" I have to hash that 800k to something smaller?)

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• Binary Trees in Scheme

  - by Javier

  Consider the following BNF defining trees of numbers. Notice that a tree can either be a leaf, a node-1 with one subtrees, or a node-2 with two subtrees. tree ::= (’leaf number) | (’node-1 tree) | (’node-2 tree tree) a. Write a template for recursive procedures on these trees. b. Define the procedure (leaf-count t) that returns the number of leaves in t > (leaf-count ’(leaf 5)) 1 > (leaf-count ’(node-2 (leaf 25) (leaf 17))) 2 > (leaf-count ’(node-1 (node-2 (leaf 4) (node-2 (leaf 2) (leaf 3))))) 3 Here's what I have so far: ;define what a leaf, node-1, and node-2 is (define leaf list) (define node-1 list) (define node-2 list) ;procedure to decide if a list is a leaf or a node (define (leaf? tree) (number? (car tree))) (define (node? tree) (pair? (car tree))) (define (leaf-count tree) (cond ((null? tree) 0) ((number? tree) 0) ((leaf? tree) 1) (else (+ (leaf-count (car tree)) (leaf-count (cdr tree)))))) It looks like it should run just fine, but when I try to run it using a simple test case like (leaf-count '(leaf 5)) I get the following error message: car: expects argument of type pair; given leaf What does this error message mean? I am defining a leaf as a list. But for some reason, it's not seeing that and gives me that error message.

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• Shift-reduce: when to stop reducing?

  - by Joey Adams

  I'm trying to learn about shift-reduce parsing. Suppose we have the following grammar, using recursive rules that enforce order of operations, inspired by the ANSI C Yacc grammar: S: A; P : NUMBER | '(' S ')' ; M : P | M '*' P | M '/' P ; A : M | A '+' M | A '-' M ; And we want to parse 1+2 using shift-reduce parsing. First, the 1 is shifted as a NUMBER. My question is, is it then reduced to P, then M, then A, then finally S? How does it know where to stop? Suppose it does reduce all the way to S, then shifts '+'. We'd now have a stack containing: S '+' If we shift '2', the reductions might be: S '+' NUMBER S '+' P S '+' M S '+' A S '+' S Now, on either side of the last line, S could be P, M, A, or NUMBER, and it would still be valid in the sense that any combination would be a correct representation of the text. How does the parser "know" to make it A '+' M So that it can reduce the whole expression to A, then S? In other words, how does it know to stop reducing before shifting the next token? Is this a key difficulty in LR parser generation?

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• MS SQL server and Trees

  - by Julian

  Im looking for some way of extrating data form a tree table as defined below. Table Tree Defined as :- TreeID uniqueidentifier TreeParent uniqueidentifier TreeCode varchar(50) TreeDesc varchar(100) Data some (23k rows), Parent Refs back into ID in table The following SQL renders the whole tree (takes arround 2 mins 30) I need to do the following. 1) Render each Tree Node with its LVL 1 parent 2) Render all nodes that have a Description that matches a TreeDesc like 'SomeText%' 3) Render all parent nodes that are for a single tree id. Items 2 and 3 take 2mins30 so this needs to be a lot faster! Item 1, just cant work out how to do it with out killing SQL or taking forever any sugestions would be helpfull Thanks Julian WITH TreeCTE(TreeCode, TreeDesc, depth, TreeParent, TreeID) AS ( -- anchor member SELECT cast('' as varchar(50)) as TreeCode , cast('Trees' as varchar(100)) as TreeDesc, cast('0' as Integer) as depth, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier) as TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier) as TreeID UNION ALL -- recursive member SELECT s.TreeCode, s.TreeDesc, cte.depth+1, isnull(s.TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)), isnull(s.TreeID, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) FROM pdTrees AS S JOIN TreeCTE AS cte ON isnull(s.TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) = isnull( cte.TreeID , cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) ) -- outer query SELECT s.TreeID, s.TreeCode, s.TreeDesc, s.depth, s.TreeParent FROM TreeCTE s

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• Why is TransactionScope operation is not valid?

  - by Cragly

  I have a routine which uses a recursive loop to insert items into a SQL Server 2005 database The first call which initiates the loop is enclosed within a transaction using TransactionScope. When I first call ProcessItem the myItem data gets inserted into the database as expected. However when ProcessItem is called from either ProcessItemLinks or ProcessItemComments I get the following error. “The operation is not valid for the state of the transaction” I am running this in debug with VS 2008 on Windows 7 and have the MSDTC running to enable distributed transactions. The code below isn’t my production code but is set out exactly the same. The AddItemToDatabase is a method on a class I cannot modify and uses a standard ExecuteNonQuery() which creates a connection then closes and disposes once completed. I have looked at other posting on here and the internet and still cannot resolve this issue. Any help would be much appreciated. using (TransactionScope processItem = new TransactionScope()) { foreach (Item myItem in itemsList) { ProcessItem(myItem); } processItem.Complete(); } private void ProcessItem(Item myItem) { AddItemToDatabase(myItem); ProcessItemLinks(myItem); ProcessItemComments(myItem); } private void ProcessItemLinks(Item myItem) { foreach (Item link in myItem.Links) { ProcessItem(link); } } private void ProcessItemComments(Item myItem) { foreach (Item comment in myItem.Comments) { ProcessItem(comment); } } Here is top part of the stack trace. Unfortunatly I cant show the build up to this point as its company sensative information which I can not disclose. Hope this is enough information. at System.Transactions.TransactionState.EnlistPromotableSinglePhase(InternalTransaction tx, IPromotableSinglePhaseNotification promotableSinglePhaseNotification, Transaction atomicTransaction) at System.Transactions.Transaction.EnlistPromotableSinglePhase(IPromotableSinglePhaseNotification promotableSinglePhaseNotification) at System.Data.SqlClient.SqlInternalConnection.EnlistNonNull(Transaction tx) at System.Data.SqlClient.SqlInternalConnection.Enlist(Transaction tx) at System.Data.SqlClient.SqlInternalConnectionTds.Activate(Transaction transaction) at System.Data.ProviderBase.DbConnectionInternal.ActivateConnection(Transaction transaction) at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject) at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) at System.Data.SqlClient.SqlConnection.Open()

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• User Control SiteMap Provider Rendering Error

  - by Serexx

  I have created a Custom Server Control that renders the SiteMap as a pure UL for CSS styling. At run-time it renders properly but in VS2008 Design View VS shows this error: Error Rendering Control - menuMainAn unhandled exception has occurred. The provider 'AspNetXmlSiteMapProvider' specified for the defaultProvider does not exist in the providers collection. I have 'AspNetXmlSiteMapProvider' specified in web.config as per here : link text While I am happy that the code runs properly, the Designer error is bothersome if the underlying issue might cause the code to break in some circumstances so I need to understand what is going on... The code explicitly references the sitemap in the Render Method with : int level = 1; string ul = string.Format("<div class='{0}' id='{1}'>{2}</div>", CssClassName, this.ID.ToString(), EnumerateNodesRecursive(SiteMap.RootNode, level)); output.Write(ul); and the recursive method called referrences SiteMap.CurrentNode. Otherwise there are no explicit sitemap references in the code. Does anyone have any ideas why Deisgner is complaining?

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• Array of paths to html lists

  - by dmsk

  I wrote a recursive function, which returns an array with the paths to all files/folders in a given path. An array is already sorted and returns the exact information i want, but i struggle to display it properly in html lists. Array_of_paths = ( [0] => /path/to/folderA/ [1] => /path/to/folderA/subfolderAA/ [2] => /path/to/folderB/ [3] => /path/to/folderB/subfolderBB/ [4] => /path/to/folderB/subfolderBB/fileBB.txt [5] => /path/to/folderB/fileB.txt [6] => /path/to/folderC/ ... ) I want to put these paths in <ul>,<li> tags to see something like this: <ul> <li>/path/to/folderA/ <ul> <li>/path/to/folderA/folderAA/</li> </ul> </li> <li>/path/to/folderB <ul> <li>/path/to/folderB/subfolderBB/ <ul> <li>/path/to/folderB/subfolderBB/fileBB.txt</li> </ul> </li> <li>/path/to/folderB/fileB.txt</li> </ul> </li> <li>/path/to/folderC/</li> </ul> = /path/to/folderA/ /path/to/folderA/folderAA/ /path/to/folderB /path/to/folderB/subfolderBB/ /path/to/folderB/subfolderBB/fileBB.txt /path/to/folderB/fileB.txt /path/to/folderC/ I managed to find a couple of similars questions, but the answers were in Ruby language. So, what's the problem solving idea behind this?

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• Debugging Key-Value-Observing overflow.

  - by Paperflyer

  I wrote an audio player. Recently I started refactored some of the communication flow to make it fully MVC-compliant. Now it crashes, which in itself is not surprising. However, it crashes after a few seconds inside the Cocoa key-value-observing routines with a HUGE stack trace of recursive calls to NSKeyValueNotifyObserver. Obviously, it is recursively observing a value and thus overflowing the NSArray that holds pending notifications. According to the stack trace, the program loops from observeValueForKeyPath to setMyValue and back. Here is the according code: - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if ([keyPath isEqual:@"myValue"] && object == myModel && [self myValue] != [myModel myValue]) { [self setMyValue:[myModel myValue]; } } and - (void)setMyValue:(float)value { myValue = value; [myModel setMyValue:value]; } myModel changes myValue every 0.05 seconds and if I log the calls to these two functions, they get called only every 0.05 seconds just as they should be, so this is working properly. The stack trace looks like this: -[MyDocument observeValueForKeyPath:ofObject:change:context:] NSKeyValueNotifyObserver NSKeyValueDidChange -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] -[MyDocument setMyValue:] _NSSetFloatValueAndNotify …repeated some ~8k times until crash Do you have any idea why I could still be spamming the KVO queue?

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• Parsec: backtracking not working

  - by Nathan Sanders

  I am trying to parse F# type syntax. I started writing an [F]Parsec grammar and ran into problems, so I simplified the grammar down to this: type ::= identifier | type -> type identifier ::= [A-Za-z0-9.`]+ After running into problems with FParsec, I switched to Parsec, since I have a full chapter of a book dedicated to explaining it. My code for this grammar is typeP = choice [identP, arrowP] identP = do id <- many1 (digit <|> letter <|> char '.' <|> char '`') -- more complicated code here later return id arrowP = do domain <- typeP string "->" range <- typeP return $ "("++domain++" -> "++range++")" run = parse (do t <- typeP eof return t) "F# type syntax" The problem is that Parsec doesn't backtrack by default, so > run "int" Right "int" -- works! > run "int->int" Left "F# type syntax" unexpected "-" expecting digit, letter, ".", "`" or end of input -- doesn't work! The first thing I tried was to reorder typeP: typeP = choice [arrowP, identP] But this just stack overflows because the grammar is left-recursive--typeP never gets to trying identP because it keeps trying arrowP over and over. Next I tried try in various places, for example: typeP = choice [try identP, arrowP] But nothing I do seems to change the basic behaviours of (1) stack overflow or (2) non-recognition of "-" following an identifier. My mistake is probably obvious to anybody who has successfully written a Parsec grammar. Can somebody point it out?

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• Undefined symbols compiling apache module mod_transform on Mac OS X

  - by Laurence Rowe

  I'm trying to compile mod_transform on Mac OS X 10.6, but get an ld error while running make. Thanks to diciu I have added some CFLAGS which resolve most of the linking problems, but I still am unable to get the apreq2 linking to work $ CFLAGS="-lxml2 -lxslt -L/opt/local/lib -lapreq2" ./configure --with-apr=/opt/local/bin/apr-1-config --with-apr-util=/opt/local/bin/apu-1-config --with-apxs=/opt/local/apache2/bin/apxs --with-apreq2=/opt/local/bin/apreq2-config ...snip... $ make $ make Making all in src /opt/local/share/apr-1/build/libtool --tag=CC --mode=link gcc -Wall -I../include -I/usr/local/include -I/usr/local/include/libxml2 -O2 -arch x86_64 -I/opt/local/include -DDARWIN -DSIGPROCMASK_SETS_THREAD_MASK -no-cpp-precomp -I/opt/local/apache2/include -I/opt/local/include/apr-1 -I/opt/local/include/apr-1 -I/opt/local/include -O2 -arch x86_64 -I/opt/local/include -DDARWIN -DSIGPROCMASK_SETS_THREAD_MASK -no-cpp-precomp -I/opt/local/apache2/include -I/opt/local/include/apr-1 -I/opt/local/include -I/opt/local/include/apr-1 -I/opt/local/include/apreq2 -I/opt/local/include/apr-1 -I/opt/local/include -lxml2 -lxslt -L/opt/local/lib -lapreq2 -module -export-dynamic -avoid-version -no-undefined /opt/local/lib/libapreq2.la -L/opt/local/lib -laprutil-1 -L/opt/local/lib/db46 -L/opt/local/lib -lapr-1 -lpthread -ldb-4.6 -lexpat -liconv -o http.la -rpath /opt/local/apache2/modules/mod_transform http_la-http.lo /usr/bin/gcc-4.2 -o .libs/http.so -bundle .libs/http_la-http.o -lxml2 -lxslt -L/opt/local/lib /opt/local/lib/libapreq2.dylib -L/opt/local/lib/db46 /opt/local/lib/libaprutil-1.dylib /opt/local/lib/libapr-1.dylib -lpthread /opt/local/lib/db46/libdb-4.6.dylib /opt/local/lib/libexpat.dylib /opt/local/lib/libiconv.dylib -arch x86_64 -arch x86_64 Undefined symbols: "_apreq_handle_apache2", referenced from: _transform_run_begin in http_la-http.o _filter_init in http_la-http.o ld: symbol(s) not found collect2: ld returned 1 exit status make[1]: *** [http.la] Error 1 make: *** [all-recursive] Error 1 Anyone have any other tweaks to fix this? This is mod_transform from http://svn.outoforder.cc/svn/mod%5Ftransform/trunk/ Laurence

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• Bubble Breaker Game Solver better than greedy?

  - by Gregory

  For a mental exercise I decided to try and solve the bubble breaker game found on many cell phones as well as an example here:Bubble Break Game The random (N,M,C) board consists N rows x M columns with C colors The goal is to get the highest score by picking the sequence of bubble groups that ultimately leads to the highest score A bubble group is 2 or more bubbles of the same color that are adjacent to each other in either x or y direction. Diagonals do not count When a group is picked, the bubbles disappear, any holes are filled with bubbles from above first, ie shift down, then any holes are filled by shifting right A bubble group score = n * (n - 1) where n is the number of bubbles in the bubble group The first algorithm is a simple exhaustive recursive algorithm which explores going through the board row by row and column by column picking bubble groups. Once the bubble group is picked, we create a new board and try to solve that board, recursively descending down Some of the ideas I am using include normalized memoization. Once a board is solved we store the board and the best score in a memoization table. I create a prototype in python which shows a (2,15,5) board takes 8859 boards to solve in about 3 seconds. A (3,15,5) board takes 12,384,726 boards in 50 minutes on a server. The solver rate is ~3k-4k boards/sec and gradually decreases as the memoization search takes longer. Memoization table grows to 5,692,482 boards, and hits 6,713,566 times. What other approaches could yield high scores besides the exhaustive search? I don't seen any obvious way to divide and conquer. But trending towards larger and larger bubbles groups seems to be one approach Thanks to David Locke for posting the paper link which talks above a window solver which uses a constant-depth lookahead heuristic.

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• Recursively adding threads to a Java thread pool

  - by Leith

  I am working on a tutorial for my Java concurrency course. The objective is to use thread pools to compute prime numbers in parallel. The design is based on the Sieve of Eratosthenes. It has an array of n bools, where n is the largest integer you are checking, and each element in the array represents one integer. True is prime, false is non prime, and the array is initially all true. A thread pool is used with a fixed number of threads (we are supposed to experiment with the number of threads in the pool and observe the performance). A thread is given a integer multiple to process. The thread then finds the first true element in the array that is not a multiple of thread's integer. The thread then creates a new thread on the thread pool which is given the found number. After a new thread is formed, the existing thread then continues to set all multiples of it's integer in the array to false. The main program thread starts the first thread with the integer '2', and then waits for all spawned threads to finish. It then spits out the prime numbers and the time taken to compute. The issue I have is that the more threads there are in the thread pool, the slower it takes with 1 thread being the fastest. It should be getting faster not slower! All the stuff on the internet about Java thread pools create n worker threads the main thread then wait for all threads to finish. The method I use is recursive as a worker can spawn more worker threads. I would like to know what is going wrong, and if Java thread pools can be used recursively.

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• How would you answer Joel's sample programming questions?

  - by Khorkrak

  I recently interviewed a candidate for a new position here. I wish though that I'd read Joel's Guerrilla Guide to Interviewing prior to that interview - naturally I happened upon it the night afterwards :P http://www.joelonsoftware.com/articles/GuerrillaInterviewing3.html So I tried answering the easy questions myself - yeah I used the python interpreter to type stuff in and tested the results a bit - I didn't look up any solutions beforehand though and I also thought about how long it took me to come up with answers for each one and what I'd look for the next time I interview someone. I'd let them type stuff into the interpreter and see how did used python's introspection capabilities too to find out things like what's the re module's method for building a regex etc. Here are my answers - these are in python of course - what are yours in your favourite language? Do you see any issues with the answers I came up with - i.e. how could they be improved upon - what did I miss? Joel's example questions: Write a function that determines if a string starts with an upper-case letter A-Z. import re upper_regex = re.compile("^[A-Z]") def starts_with_upper(text): return upper_regex.match(text) is not None Write a function that determines the area of a circle given the radius. from math import pi def area(radius): return pi * radius**2 Add up all the values in an array. sum([1, 2, 3, 4, 5]) Harder Question: Write an example of a recursive function - so how about the classic factorial one: def factorial(num): if num > 1: return num * factorial(num - 1) else: return 1

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• PostgreSQL: Auto-partition a table

  - by Adam Matan

  Hi, I have a huge database which holds pairs of numbers (A,B), each ranging from 0 to 10,000 and stored as floats. e.g., (1, 9984.4), (2143.44, 124.243), (0.55, 0), ... Since the PostgreSQL table which stores these pairs grew quite large, I have decided to partition it into inheriting sub-tables. I intend to create 100 such tables, each storing a range of 1000x1000. The problem is that these numbers tend to come in large chunks of nearby numbers. It means that in the future, some tables will be nearly empty and some will hold a very large portion of the database. Unfortunately, the distribution of future pairs is yet unknown. I am looking for a way to automatically repartition my table. That means that if a certain subtable holds more than a specific number of pairs, it will be automatically partitioned into four sub-sub tables, and so on. My questions are: Is recursive partitioning and inheritance possible in PostgreSQL 8.3? Will indexes and query plans understand it? What's the best way to split a subtable once it grew too large? I should point out that this isn't a live database, so a downtime of few hours every week is totally acceptable. Thanks in advance, Adam

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• Beginner problems with references to arrays in python 3.1.1

  - by Protean

  As part of the last assignment in a beginner python programing class, I have been assigned a traveling sales man problem. I settled on a recursive function to find each permutation and the sum of the distances between the destinations, however, I am have a lot of problems with references. Arrays in different instances of the Permute and Main functions of TSP seem to be pointing to the same reference. from math import sqrt class TSP: def __init__(self): self.CartisianCoordinates = [['A',[1,1]], ['B',[2,2]], ['C',[2,1]], ['D',[1,2]], ['E',[3,3]]] self.Array = [] self.Max = 0 self.StoredList = ['',0] def Distance(self, i1, i2): x1 = self.CartisianCoordinates[i1][1][0] y1 = self.CartisianCoordinates[i1][1][1] x2 = self.CartisianCoordinates[i2][1][0] y2 = self.CartisianCoordinates[i2][1][1] return sqrt(pow((x2 - x1), 2) + pow((y2 - y1), 2)) def Evaluate(self): temparray = [] Data = [] for i in range(len(self.CartisianCoordinates)): Data.append([]) for i1 in range(len(self.CartisianCoordinates)): for i2 in range(len(self.CartisianCoordinates)): if i1 != i2: temparray.append(self.Distance(i1, i2)) else: temparray.append('X') Data[i1] = temparray temparray = [] self.Array = Data self.Max = len(Data) def Permute(self,varray,index,vcarry,mcarry): #Problem Class array = varray[:] carry = vcarry[:] for i in range(self.Max): print ('ARRAY:', array) print (index,i,carry,array[index][i]) if array[index][i] != 'X': carry[0] += self.CartisianCoordinates[i][0] carry[1] += array[index][i] if len(carry) != self.Max: temparray = array[:] for j in range(self.Max):temparray[j][i] = 'X' index = i mcarry += self.Permute(temparray,index,carry,mcarry) else: return mcarry print ('pass',mcarry) return mcarry def Main(self): out = [] self.Evaluate() for i in range(self.Max): array = self.Array[:] #array appears to maintain the same reference after each copy, resulting in an incorrect array being passed to Permute after the first iteration. print (self.Array[:]) for j in range(self.Max):array[j][i] = 'X' print('I:', i, array) out.append(self.Permute(array,i,[str(self.CartisianCoordinates[i][0]),0],[])) return out SalesPerson = TSP() print(SalesPerson.Main()) It would be greatly appreciated if you could provide me with help in solving the reference problems I am having. Thank you.

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• StackOverFlowException - but oviously NO recursion/endless loop

  - by user567706

  Hi there, I'm now blocked by this problem the entire day, read thousands of google results, but nothing seems to reflect my problem or even come near to it... i hope any of you has a push into the right direction for me. I wrote a client-server-application (so more like 2 applications) - the client collects data about his system, as well as a screenshot, serializes all this into a XML stream (the picture as a byte[]-array]) and sends this to the server in regular intervals. The server receives the stream (via tcp), deserializes the xml to an information-object and shows the information on a windows form. This process is running stable for about 20-25 minutes at a submission interval of 3 seconds. When observing the memory usage there's nothing significant to see, also kinda stable. But after these 20-25 mins the server throws a StackOverflowException at the point where it deserializes the tcp-stream, especially when setting the Image property from the byte[]-array. I thoroughly searched for recursive or endless loops, and regarding the fact that it occurs after thousands of sucessfull intervals, i could hardly imagine that. public byte[] ImageBase { get { MemoryStream ms = new MemoryStream(); _screen.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg); return ms.GetBuffer(); } set { if (_screen != null) _screen.Dispose(); //preventing well-known image memory leak MemoryStream ms = new MemoryStream(value); try { _screen = Image.FromStream(ms); //<< EXCEPTION THROWING HERE } catch (StackOverflowException ex) //thx to new CLR management this wont work anymore -.- { Console.WriteLine(ex.Message + Environment.NewLine + ex.StackTrace); } ms.Dispose(); ms = null; } } I hope that more code would be unnecessary, or it could get very complex... Please help, i have no clue at all anymore thx Chris

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• Scheme Infix to Postfix

  - by Cody

  Let me establish that this is part of a class assignment, so I'm definitely not looking for a complete code answer. Essentially we need to write a converter in Scheme that takes a list representing a mathematical equation in infix format and then output a list with the equation in postfix format. We've been provided with the algorithm to do so, simple enough. The issue is that there is a restriction against using any of the available imperative language features. I can't figure out how to do this in a purely functional manner. This is our fist introduction to functional programming in my program. I know I'm going to be using recursion to iterate over the list of items in the infix expression like such. (define (itp ifExpr) ( ; do some processing using cond statement (itp (cdr ifExpr)) )) I have all of the processing implemented (at least as best I can without knowing how to do the rest) but the algorithm I'm using to implement this requires that operators be pushed onto a stack and used later. My question is how do I implement a stack in this function that is available to all of the recursive calls as well?

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• Reordering arguments using recursion (pro, cons, alternatives)

  - by polygenelubricants

  I find that I often make a recursive call just to reorder arguments. For example, here's my solution for endOther from codingbat.com: Given two strings, return true if either of the strings appears at the very end of the other string, ignoring upper/lower case differences (in other words, the computation should not be "case sensitive"). Note: str.toLowerCase() returns the lowercase version of a string. public boolean endOther(String a, String b) { return a.length() < b.length() ? endOther(b, a) : a.toLowerCase().endsWith(b.toLowerCase()); } I'm very comfortable with recursions, but I can certainly understand why some perhaps would object to it. There are two obvious alternatives to this recursion technique: Swap a and b traditionally public boolean endOther(String a, String b) { if (a.length() < b.length()) { String t = a; a = b; b = t; } return a.toLowerCase().endsWith(b.toLowerCase()); } Not convenient in a language like Java that doesn't pass by reference Lots of code just to do a simple operation An extra if statement breaks the "flow" Repeat code public boolean endOther(String a, String b) { return (a.length() < b.length()) ? b.toLowerCase().endsWith(a.toLowerCase()) : a.toLowerCase().endsWith(b.toLowerCase()); } Explicit symmetry may be a nice thing (or not?) Bad idea unless the repeated code is very simple ...though in this case you can get rid of the ternary and just || the two expressions So my questions are: Is there a name for these 3 techniques? (Are there more?) Is there a name for what they achieve? (e.g. "parameter normalization", perhaps?) Are there official recommendations on which technique to use (when)? What are other pros/cons that I may have missed?

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• Maintain one to one mapping between objects

  - by Rohan West

  Hi there, i have the following two classes that provide a one to one mapping between each other. How do i handle null values, when i run the second test i get a stackoverflow exception. How can i stop this recursive cycle? Thanks [TestMethod] public void SetY() { var x = new X(); var y = new Y(); x.Y = y; Assert.AreSame(x.Y, y); Assert.AreSame(y.X, x); } [TestMethod] public void SetYToNull() { var x = new X(); var y = new Y(); x.Y = y; y.X = null; Assert.IsNull(x.Y); Assert.IsNull(y.X); } public class X { private Y _y; public Y Y { get { return _y; } set { if(_y != value) { if(_y != null) { _y.X = null; } _y = value; if(_y != null) { _y.X = this; } } } } } public class Y { private X _x; public X X { get { return _x; } set { if (_x != value) { if (_x != null) { _x.Y = null; } _x = value; if (_x != null) { _x.Y = this; } } } } }

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• How to use Common Table Expression and check no duplication in sqlserver

  - by vodkhang

  I have a table references to itself. User table: id, username, managerid and managerid links back to id Now, I want to get all the managers including direct manager, manager of direct manager, so on and so forth... The problem is that I do not want to have a unstop recursive sql. So, I want to check if an id alreay in a list, I will not include it anymore. Here is my sql for that: with --the relation for all the subparts of ozsolar including itself all_managers (id, username, managerid, idlist) as ( --seed that is the ozsola part select u1.id, u1.username, u1.managerid, ' ' from users u1, users u2 where u1.id = u2.managerid and u2.id = 6 UNION ALL select u.id, u.username, u.managerid, idlist + ' ' + u.id from all_managers a, users u where a.managerid = u.id and charindex(cast(u.id as nvarchar(5)), idlist) != 0 ) --select the total number of subparts and group by subpart select id, username from all_managers; The problem is that in this line: select u1.id, u1.username, u1.managerid, ' ' The sqlserver complains with me that I can not put ' ' as the initialized for idlist. nvarchar(40) does not work as well. I do not know how to declare it inside a common table expression like this one. Usually, in db2, I can just put varchar(40)

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