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• SIP UAS asks for OPTIONS

  - by TacB0sS

  Hey, I have UAC that registers to a UAS, after registration the UAS sends me an OPTIONS request, what should I answer it? only the audio media streams? Update I: Allow me to explain myself better... if I want to invite someone to a session I USE the INVITE method and negotiate the media then, for that specific session. But once I register to the server, and it asks me for OPTIONS, then what should I supply, everything my client supports? once I answer it would it deduce that every INVITE I would request from now on would use these medias? or would I need to supply new media with every request? Update II: Hi Wiz, I was in the process of building a negotiation system, so i tried it out and replied the UAS here is the sort dialog we had: OPTIONS sip:[email protected] SIP/2.0 Via: SIP/2.0/UDP xx.xx.xx.xx:5060;branch=z9hG4bK45b197cb;rport=5060;received=xx.xx.xx.xx From: "Unknown" <sip:[email protected]>;tag=as66cf26df To: <sip:[email protected]> Contact: <sip:[email protected]> Call-ID: [email protected] CSeq: 102 OPTIONS User-Agent: Freeswitch 1.2.3 Max-Forwards: 70 Date: Sat, 05 Jun 2010 12:06:43 GMT Allow: INVITE,ACK,CANCEL,OPTIONS,BYE,REFER,SUBSCRIBE,NOTIFY,INFO Supported: replaces Content-Length: 0 OPTIONS In Response To 102: SIP/2.0 200 OK Via: SIP/2.0/UDP xx.xx.xx.xx:5060;branch=z9hG4bK45b197cb;rport=5060;received=xx.xx.xx.xx From: "Unknown" <sip:[email protected]>;tag=as66cf26df To: <sip:[email protected]> CSeq: 102 OPTIONS Call-ID: [email protected] Allow: INVITE,CANCEL,ACK,BYE,OPTIONS Content-Type: application/sdp Content-Length: 248 v=0 o=310 4515233118481497946 4515233118481497946 IN IP4 10.0.0.1 s=- i=Nu-Art Software - TacB0sS VoIP information c=IN IP4 10.0.0.1 m=audio 40000 RTP/AVP 0 8 101 a=rtpmap:0 PCMU/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:101 telephone-event/8000 This response caused the server to stop sending me the options request, does this means I can only use these parameters with the server now? or as you said, it does not matter? Thanks, Adam.

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• Modeling complex hierarchies

  - by jdn

  To gain some experience, I am trying to make an expert system that can answer queries about the animal kingdom. However, I have run into a problem modeling the domain. I originally considered the animal kingdom hierarchy to be drawn like -animal -bird -carnivore -hawk -herbivore -bluejay -mammals -carnivores -herbivores This I figured would allow me to make queries easily like "give me all birds", but would be much more expensive to say "give me all carnivores", so I rewrote the hierarchy to look like: -animal -carnivore -birds -hawk -mammals -xyz -herbivores -birds -bluejay -mammals But now it will be much slower to query "give me all birds." This is of course a simple example, but it got me thinking that I don't really know how to model complex relationships that are not so strictly hierarchical in nature in the context of writing an expert system to answer queries as stated above. A directed, cyclic graph seems like it could mathematically solve the problem, but storing this in a relational database and maintaining it (updates) would seem like a nightmare to me. I would like to know how people typically model such things. Explanations or pointers to resources to read further would be acceptable and appreciated.

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• Using Hibernate with MS ACCESS 2007 Database (Free JDBC Driver)

  - by Quentin T.

  1. I want to do a reverse engineering action with the Hibernate plugin of Eclipse on a MS Access 2007 Database. I'm forced to use a existing MS Access 2007 db. A easy solution is to buy the HXTT. But I want to use a free driver to do my work. So I tried to apply this post : http://www.programmingforfuture.com/2011/06/how-to-use-ms-access-with-hibernate.html (That uses the SQL Server dialect and the driver sun.jdbc.odbc.JdbcOdbcDriver) Unfortunately I have an error that nobody seems to have been on the internet: Exception while generating code Reason : org.hibernate.exception.GenericJDBCException: Error while reading primary key meta data for `c:/myaccessdb.mdb`.TableTest1 I have try to change the primary key on my MS Access DB (deleting all primary key) or to try the reverse engineering on a MS ACCESS with only one table without primary key, but I got all times the problems. 2. The purpose of my job is to transfer daily (weekly) an Oracle 11g database with data from an existing database MS ACCESS 2007. And I thought to use a procedure (Hibernate EJB) Java to be launched automatically every week to do the data transfer. Is this is the best solution ? Configuration : sun.jdbc.odbc.JdbcOdbcDriver v??? Hibernate v3.4 Eclipse ps: If you are a HXTT developer or seller please be indulgent with my post ;). Making money by making people believe that you help, it's bad ! A solution is to use Derby Client driver, as the solution in the post: Does anyone know if Hibernate and java will work effectively with Access? But a clarification of the answer of Rich Seller is required. Could you explain your answer and explain your configuration (hibernate.cfg.xml, persistence.xml and what URL you use in the property name="hibernate.connection.url") without using paying HXTT driver but with the free Derby driver.

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• Requirements for connecting to Oracle with JDBC?

  - by Lord Torgamus

  I'm a newbie to Java-related web development, and I can't seem to get a simple program with JDBC working. I'm using off-the-shelf Oracle 10g XE and the Eclipse EE IDE. From the books and web pages I've checked so far, I've narrowed the problem down to either an incorrectly written database URL or a missing JAR file. I'm getting the following error: java.sql.SQLException: No suitable driver found for jdbc:oracle://127.0.0.1:8080 with the following code: import java.sql.*; public class DatabaseTestOne { public static void main(String[] args) { String url = "jdbc:oracle://127.0.0.1:8080"; String username = "HR"; String password = "samplepass"; String sql = "SELECT EMPLOYEE_ID FROM EMPLOYEES WHERE LAST_NAME='King'"; Connection connection; try { connection = DriverManager.getConnection(url, username, password); Statement statement = connection.createStatement(); System.out.println(statement.execute(sql)); connection.close(); } catch (SQLException e) { System.err.println(e); } } } What is the proper format for a database URL, anyways? They're mentioned a lot but I haven't been able to find a description. Thanks! EDIT (the answer): Based on duffymo's answer, I got ojdbc14.jar from http://www.oracle.com/technology/software/tech/java/sqlj_jdbc/htdocs/jdbc_10201.html and dropped it in the Eclipse project's Referenced Libraries. Then I changed the start of the code to ... try { Class.forName("oracle.jdbc.driver.OracleDriver"); } catch (ClassNotFoundException e) { System.err.println(e); } // jdbc:oracle:thin:@<hostname>:<port>:<sid> String url = "jdbc:oracle:thin:@GalacticAC:1521:xe"; ... and it worked.

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• Access class instance "name" dynamically in Python

  - by user328317

  In plain english: I am creating class instances dynamically in a for loop, the class then defines a few attributes for the instance. I need to later be able to look up those values in another for loop. Sample code: class A: def init(self, name, attr): self.name=name self.attr=attr names=("a1", "a2", "a3") x=10 for name in names: name=A(name, x) x += 1 ... ... ... for name in names: print name.attr How can I create an identifier for these instances so they can be accessed later on by "name"? I've figured a way to get this by associating "name" with the memory location: class A: instances=[] names=[] def init(self, name, attr): self.name=name self.attr=attr A.instances.append(self) A.names.append(name) names=("a1", "a2", "a3") x=10 for name in names: name=A(name, x) x += 1 ... ... ... for name in names: index=A.names.index(name) print "name: " + name print "att: " + str(A.instances[index].att) This has had me scouring the web for 2 days now, and I have not been able to find an answer. Maybe I don't know how to ask the question properly, or maybe it can't be done (as many other posts seemed to be suggesting). Now this 2nd example works, and for now I will use it. I'm just thinking there has to be an easier way than creating your own makeshift dictionary of index numbers and I'm hoping I didn't waste 2 days looking for an answer that doesn't exist. Anyone have anything? Thanks in advance, Andy Update: A coworker just showed me what he thinks is the simplest way and that is to make an actual dictionary of class instances using the instance "name" as the key.

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• Read specific line from text file, according to Checked Listbox selection number.

  - by Manolis

  Heya, i want to create an application which will read a specific line from a text file and show it in a textbox. The line will be chosen according to the number of the listbox selection i will make. Here's the code: Public Class Form1 Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load End Sub Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim i As Integer For i = 0 To Me.CheckedListBox1.CheckedIndices.Count - 1 Me.CheckedListBox1.SetItemChecked(Me.CheckedListBox1.CheckedIndices(0),False) Next i End Sub Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click If CheckedListBox1.CheckedItems.Count <> 0 Then Dim reader As New System.IO.StreamReader(CurDir() & "\" & "READ.txt") Dim x As Integer Dim s As String = "" For x = 0 To CheckedListBox1.CheckedItems.Count - 1 s = s & "Answer " & (x + 1).ToString & ") " & CheckedListBox1.CheckedItems(x).ToString & ControlChars.CrLf & reader.ReadLine() & ControlChars.CrLf & ControlChars.CrLf Next x Answer.Text = (s) Else MessageBox.Show("Please select questions.", "Error", _ MessageBoxButtons.OK, _ MessageBoxIcon.Information) Return End If End Sub End Class So lets say i 'check' the first, second, and fifth items from the checked listbox, i want it to read from the text file the first, second, and fifth lines of text and show them in the textbox. The current code just reads line 1, 2, 3 (...) in order, no matter what item i have 'checked'. Thanks in advance!

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• Ruby on Rails Mongrel web server stuck when MySQL service is running

  - by Marcos Buarque

  Hi, I am a Ruby on Rails newbie and already have a problem. I have started the Mongrel web server and it works fine when MySQL service isn't running. But when MySQL is on, Mongrel stucks. It ceases from serving the pages. So far, I have tested the localhost:3000 URL. When MySQL is off, it serves the page. When I click "about application's environment", I get the messasge (of course) "Can't connect to MySQL server on 'localhost' (10061)". After starting the MySQL service and refreshing, I get no more answer and Mongrel does not serve the webpage. It gets stuck with no answer to the browser. Then I have to stop the webserver and restart it. I have installed mysql2 gem with the command gem install mysql2. I was able to create the _test and _development databases with the command line rake db:create. I have tested with MySQL root user and blank password and also tried with a superuser user I have created. No success. Here is the server log: ======================== Started GET "/rails/info/properties" for 127.0.0.1 at Fri Dec 24 17:41:25 -0200 2010 Mysql2::Error (Can't connect to MySQL server on 'localhost' (10061)): Rendered C:/Ruby187/lib/ruby/gems/1.8/gems/actionpack-3.0.3/lib/action_dispatch/middleware/templates/rescues/_trace.erb (1.0ms) Rendered C:/Ruby187/lib/ruby/gems/1.8/gems/actionpack-3.0.3/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb (5.0ms) Rendered C:/Ruby187/lib/ruby/gems/1.8/gems/actionpack-3.0.3/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb within rescues/layout (35.0ms) ================= I am running on a Windows 7 environment with firewall down.

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• POST XML to server, receive PDF

  - by Shaggy Frog

  Similar to this question, we are developing a Web app where the client clicks a button to receive a PDF from the server. Right now we're using the .ajax() method with jQuery to POST the data the backend needs to generate the PDF (we're sending XML) when the button is pressed, and then the backend is generating the PDF entirely in-memory and sending it back as application/pdf in the HTTP response. One answer to that question requires the server-side save the PDF to disk so it can give back a URL for the client to GET. But I don't want the backend caching content at all. The other answer suggests the use of a jQuery plugin, but when you look at its code, it's actually generating a form element and then submitting the form. That method will not work for us since we are sending XML data in the body of the HTTP request. Is there a way to have the browser open up the PDF without caching the PDF server-side, and without requiring us to throw out our send-data-to-the-server-using-XML solution? (I'd like the browser to behave like it does when a form element is submitted -- a POST is made and then the browser looks at the Content-type header to determine what to do next, like load the PDF in the browser window, a la Safari)

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• Building a ctypes-"based" C library with distutils

  - by Robie Basak

  Following this recommendation, I have written a native C extension library to optimise part of a Python module via ctypes. I chose ctypes over writing a CPython-native library because it was quicker and easier (just a few functions with all tight loops inside). I've now hit a snag. If I want my work to be easily installable using distutils using python setup.py install, then distutils needs to be able to build my shared library and install it (presumably into /usr/lib/myproject). However, this not a Python extension module, and so as far as I can tell, distutils cannot do this. I've found a few references to people other people with this problem: Someone on numpy-discussion with a hack back in 2006. Somebody asking on distutils-sig and not getting an answer. Somebody asking on the main python list and being pointed to the innards of an existing project. I am aware that I can do something native and not use distutils for the shared library, or indeed use my distribution's packaging system. My concern is that this will limit usability as not everyone will be able to install it easily. So my question is: what is the current best way of distributing a shared library with distutils that will be used by ctypes but otherwise is OS-native and not a Python extension module? Feel free to answer with one of the hacks linked to above if you can expand on it and justify why that is the best way. If there is nothing better, at least all the information will be in one place.

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• confused about how to use JSON in C#

  - by Josh

  The answer to just about every single question about using C# with json seems to be "use JSON.NET" but that's not the answer I'm looking for. the reason I say that is, from everything I've been able to read in the documentation, JSON.NET is basically just a better performing version of the DataContractSerializer built into the .net framework... Which means if I want to deserialize a JSON string, I have to define the full, strongly-typed class for EVERY request I might have. so if I have a need to get categories, posts, authors, tags, etc, I have to define a new class for every one of these things. This is fine if I built the client and know exactly what the fields are, but I'm using someone else's api, so I have no idea what the contract is unless I download a sample response string and create the class manually from the JSON string. Is that the only way it's done? Is there not a way to have it create a kind of hashtable that can be read with json["propertyname"]? Finally, if I do have to build the classes myself, what happens when the API changes and they don't tell me (as twitter seems to be notorious for doing)? I'm guessing my entire project will break until I go in and update the object properties... So what exactly is the general workflow when working with JSON? And by general I mean library-agnostic. I want to know how it's done in general, not specifically to a target library... I hope that made sense, this has been a very confusing area to get into... thanks!

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• Easiest way to plot values as symbols in scatter plot?

  - by AllenH

  In an answer to an earlier question of mine regarding fixing the colorspace for scatter images of 4D data, Tom10 suggested plotting values as symbols in order to double-check my data. An excellent idea. I've run some similar demos in the past, but I can't for the life of me find the demo I remember being quite simple. So, what's the easiest way to plot numerical values as the symbol in a scatter plot instead of 'o' for example? Tom10 suggested plt.txt(x,y,value)- and that is the implementation used in a number of examples. I however wonder if there's an easy way to evaluate "value" from my array of numbers? Can one simply say: str(valuearray) ? Do you need a loop to evaluate the values for plotting as suggested in the matplotlib demo section for 3D text scatter plots? Their example produces: However, they're doing something fairly complex in evaluating the locations as well as changing text direction based on data. So, is there a cute way to plot x,y,C data (where C is a value often taken as the color in the plot data- but instead I wish to make the symbol)? Again, I think we have a fair answer to this- I just wonder if there's an easier way?

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• Setup SVN/LAMP/Test Server/ on linux, where to start?

  - by John Isaacks

  I have a ubuntu machine I have setup. I installed apache2 and php5 on it. I can access the web server from other machines on the network via http://linux-server. I have subversion installed on it. I also have vsftpd installed on it so I can ftp to it from another computer on the network. Myself and other users currently use dreamweaver to checkin-checkout files directly from our live site to make changes. I want the connect to the linux server from pc. make the changes on the test server until ready and then pushed to the live site. I want to use subversion also into this workflow as well. but not sure what the best workflow is or how to set this up. I have no experience with linux, svn, or even using a test server, the checkin/out we are currently doing is the way I have always done it. I have hit many snags already just getting what I have setup because of my lack of knowledge in the area. Dreamweaver 5 has integration with subversion but I can't figure out how to get it to work. I want to setup and create the best workflow possible. I dont expect anyone to be able to give me an answer that will enlighten me enough to know everthing I need to know to do what I want to do (altough if possible that would be great) instead I am looking for maybe a knowledge path like answer. Like a general outline of what I need to do accompanied with links to learn how to do it. like read this book to learn linux, then read this article to learn svn, etc., then you should know what to do. I would be happy just getting it all setup, but I would like to know what I am actually doing while setting it up too.

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• Visual studio feature - commenting code Ctrl K - Ctrl C

  - by Michael

  I commented on this answer some time ago regarding how visual studio comments out code with // or /* */. I was thinking to revise the answer (to include my findings) but I had to test it first, which kind of confused me. My finding is that depending on where your marker is when you press Ctrl - K, Ctrl - C you will get either // or /* */. So I tried it out on the following code: [1] [2]FD_ZERO(&mFSet); FD_SET(user->mSender, &mFSet); timeval zeroTime = { 0, 0 }; int sel = select(0, NULL, &mFSet, NULL, &zeroTime); [3] if (sel == SOCKET_ERROR){ [5]return false; [4] } if (sel == 0){ [6] return false; [7] } The [x] is markerpositions. All [1] positions give // for all marked lines. However Start position End Position: gives: [2] [3] : /* */ [2] [4] : // [2] [5] : /* */ [2] [more than 5] : // [5] [6] : /* */ [5] [7] : // I guess it has to do with forward indentation (not backwards), that whenever code is indented more than the starting line you get // except when you haven't selected any text on the indented line ([2] [5]). But why the distinction? Why not use /* */ for when you start at [2] and // when you start at [1]?

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• Extract the vb code associated with a macro attached to an Action button in PowerPoint

  - by Patricker

  I have about 25 PowerPoint presentations, each with at least 45 slides. On each slide is a question with four possible answers and a help button which provides a hint relevant to the question. Each of the answers and the help button is a PowerPoint Action button that launches a macro. I am attempting to migrate all the questions/answers/hints into a SQL Database. I've worked with Office.Interop before when working with Excel and Word and I have plenty of SQL DB experience, so I don't foresee any issues with actually extracting the text portion of the question and answer and putting it into the db. What I have no idea how to do is given an object on a slide - get the action button info - Get the macro name - and finally get the macro's vb code. From there I can figure out how to parse out which is the correct answer and what the text of the hint is. Any help/ideas would be greatly appreciated. The guy I'm doing this for said he is willing to do it by hand... but that would take a while.

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• Beginner Question: For extract a large subset of a table from MySQL, how does Indexing, order of tab

  - by chongman

  Sorry if this is too simple, but thanks in advance for helping. This is for MySQL but might be relevant for other RDMBSs tblA has 4 columns: colA, colB, colC, mydata, A_id It has about 10^9 records, with 10^3 distinct values for colA, colB, colC. tblB has 3 columns: colA, colB, B_id It has about 10^4 records. I want all the records from tblA (except the A_id) that have a match in tblB. In other words, I want to use tblB to describe the subset that I want to extract and then extract those records from tblA. Namely: SELECT a.colA, a.colB, a.colC, a.mydata FROM tblA as a INNER JOIN tblB as b ON a.colA=b.colA a.colB=b.colB ; It's taking a really long time (more than an hour) on a newish computer (4GB, Core2Quad, ubuntu), and I just want to check my understanding of the following optimization steps. ** Suppose this is the only query I will ever run on these tables. So ignore the need to run other queries. Now my questions: 1) What indexes should I create to optimize this query? I think I just need a multiple index on (colA, colB) for both tables. I don't think I need separate indexes for colA and colB. Another stack overflow article (that I can't find) mentioned that when adding new indexes, it is slower when there are existing indexes, so that might be a reason to use the multiple index. 2) Is INNER JOIN correct? I just want results where a match is found. 3) Is it faster if I join (tblA to tblB) or the other way around, (tblB to tblA)? This previous answer says that the optimizer should take care of that. 4) Does the order of the part after ON matter? This previous answer say that the optimizer also takes care of the execution order.

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• Division by zero: Undefined Behavior or Implementation Defined in C and/or C++ ?

  - by SiegeX

  Regarding division by zero, the standards say: C99 6.5.5p5 - The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined. C++03 5.6.4 - The binary / operator yields the quotient, and the binary % operator yields the remainder from the division of the first expression by the second. If the second operand of / or % is zero the behavior is undefined. If we were to take the above paragraphs at face value, the answer is clearly Undefined Behavior for both languages. However, if we look further down in the C99 standard we see the following paragraph which appears to be contradictory(1): C99 7.12p4 - The macro INFINITY expands to a constant expression of type float representing positive or unsigned infinity, if available; Do the standards have some sort of golden rule where Undefined Behavior cannot be superseded by a (potentially) contradictory statement? Barring that, I don't think it's unreasonable to conclude that if your implementation defines the INFINITY macro, division by zero is defined to be such. However, if your implementation does not define such a macro, the behavior is Undefined. I'm curious what the consensus on this matter for each of the two languages. Would the answer change if we are talking about integer division int i = 1 / 0 versus floating point division float i = 1.0 / 0.0 ? Note (1) The C++03 standard talks about the library which includes the INFINITY macro.

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• mmap only needed pages of kernel buffer to user space

  - by axeoth

  See also this answer: http://stackoverflow.com/a/10770582/1284631 I need something similar, but without having to allocate a buffer: the buffer is large, in theory, but the user space program only needs to access some parts of it (it mocks some registers of a hardware). As I cannot allocate with vmalloc_user() such a large buffer (kernel 32 bit, in embedded environment, no swap...), I followed the same approach as in the quoted answer, trying to allocate only those pages that are really requested by the user space. So: I use a my_mmap() function for the device file (actually, is the .mmap field of a struct uio_info) to set up the fields of the vma, then, in the vm_area_struct's .fault field (also named my_fault()), I should return a page. except that: In the my_fault() method of vm_area_struct, I cannot obtain a page through: vmf->page=vmalloc_to_page(my_buf + (vmf->pgoff << PAGE_SHIFT)); since there is no allocated buffer: my_buf = vmalloc_user(MY_BUF_SIZE); fails with "allocation failed: out of vmalloc space - use vmalloc= to increase size." (and there is no room or swap to increase that vmalloc= parameter). So, I would need to get a page from the kernel and fill the vmf->page field. How to allocate a page (I assume that the offset of the page is known, as it is vm->pgoff). What base memory should I use instead of my_buf? PS: I also did set up the vma->flags |= VM_NORESERVE; (in the my_mmap()), but not sure if it helps. Is there any vmalloc_user_unreserved()-like function? (let's say, lazy allocation) Also, writing 1 to /proc/sys/vm/overcommit_memory and large values (eg 500) to /proc/sys/vm/overcommit_ratio before trying to my_buf=vmalloc_user(<large_size>) didn't work.

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• How to solve generic algebra using solver/library programmatically? Matlab, Mathematica, Wolfram etc?

  - by DevDevDev

  I'm trying to build an algebra trainer for students. I want to construct a representative problem, define constraints and relationships on the parameters, and then generate a bunch of Latex formatted problems from the representation. As an example: A specific question might be: If y < 0 and (x+3)(y-5) = 0, what is x? Answer (x = -3) I would like to encode this as a Latex formatted problem like. If $y<0$ and $(x+constant_1)(y+constant_2)=0$ what is the value of x? Answer = -constant_1 And plug into my problem solver constant_1 > 0, constant_1 < 60, constant_1 = INTEGER constant_2 < 0, constant_2 > -60, constant_2 = INTEGER Then it will randomly construct me pairs of (constant_1, constant_2) that I can feed into my Latex generator. Obviously this is an extremely simple example with no real "solving" but hopefully it gets the point across. Things I'm looking for ideally in priority order * Solve algebra problems * Definition of relationships relatively straight forward * Rich support for latex formatting (not just writing encoded strings) Thanks!

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• Number of simple mutations to change one string to another?

  - by mstksg

  Hi; I'm sure you've all heard of the "Word game", where you try to change one word to another by changing one letter at a time, and only going through valid English words. I'm trying to implement an A* Algorithm to solve it (just to flesh out my understanding of A*) and one of the things that is needed is a minimum-distance heuristic. That is, the minimum number of one of these three mutations that can turn an arbitrary string a into another string b: 1) Change one letter for another 2) Add one letter at a spot before or after any letter 3) Remove any letter Examples aabca => abaca: aabca abca abaca = 2 abcdebf => bgabf: abcdebf bcdebf bcdbf bgdbf bgabf = 4 I've tried many algorithms out; I can't seem to find one that gives the actual answer every time. In fact, sometimes I'm not sure if even my human reasoning is finding the best answer. Does anyone know any algorithm for such purpose? Or maybe can help me find one? Thanks.

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• Rails - Scalable calculation model

  - by H O

  I currently have a calculation structure in my rails app that has models metric, operand and operation_type. Presently, the metric model has many operands, and can perform calculations based on the operation_type (e.g. sum, multiply, etc.), and each operand is defined as being right or left (i.e. so that if the operation is division, the numerator and denominator can be identified). Presently, an operand is always an attribute of some model, e.g. @customer.sales.selling_price.sum. In order to make this scalable, in need to allow an operand to be either an attribute of some kind, or the results of a previous operation, i.e. an operand can be a metric. I have included a diagram of how my models currently look: Can anyone assist me with the most elegant way of allowing an operand to be an actual operand, or another metric? Thanks! EDIT: It seems based on the only answer so far that perhaps polymorphic associations are the way to go on this, but the answer is so brief I have no idea how they could be used in this way - can anyone elaborate? EDIT 2: OK, I think I'm getting somewhere - essentially i presently have a metric, which has_many operands, and an operand has_many metrics. I need a polymorphic self join, where a metric can also have many metrics - do I need to call this something else, perhaps calculated_metrics, so that the metric model can use itself? That would leave me with a situation where a metric has_many operands, and a metric has many calculated_metrics.

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• Vim: Making Auto-Completion Smarter

  - by Rafid K. Abdullah

  I use ctags, taglist, etc., to have auto completion in Vim. However, it is very limited compared to Visual Studio intellisense or Eclipse auto-completion. I am wondering whether it is possible to tune Vim to: Show auto-completion whenever . or - are typed. But only after some text that might be a variable (e.g. avoid showing auto completion after a number). Show function parameters when ( is typed. Stop removing the auto completion list when some delete all characters after . or -: When I enter a variable name, then press . or - to search for a certain member, I frequently have to delete all the characters I type after the . or -, but this makes Vim hide the auto completion list. I would like to keep it visible unless I press Esc. Showing related auto completion: When I type a variable and press ^X ^O, it usually shows me all the tags in the ctags file. I would like to have it showing only the tags related to the variable. Thanks for the help. EDIT: Some people are voting for this question, but no body seems to know the answer. So just wanted to mention that you don't have to provide a complete answer; partial answers to any of the mentioned points would be good also.

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• Reversible numerical calculations in Prolog

  - by user8472

  While reading SICP I came across logic programming chapter 4.4. Then I started looking into the Prolog programming language and tried to understand some simple assignments in Prolog. I found that Prolog seems to have troubles with numerical calculations. Here is the computation of a factorial in standard Prolog: f(0, 1). f(A, B) :- A > 0, C is A-1, f(C, D), B is A*D. The issues I find is that I need to introduce two auxiliary variables (C and D), a new syntax (is) and that the problem is non-reversible (i.e., f(5,X) works as expected, but f(X,120) does not). Naively, I expect that at the very least C is A-1, f(C, D) above may be replaced by f(A-1,D), but even that does not work. My question is: Why do I need to do this extra "stuff" in numerical calculations but not in other queries? I do understand (and SICP is quite clear about it) that in general information on "what to do" is insufficient to answer the question of "how to do it". So the declarative knowledge in (at least some) math problems is insufficient to actually solve these problems. But that begs the next question: How does this extra "stuff" in Prolog help me to restrict the formulation to just those problems where "what to do" is sufficient to answer "how to do it"?

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• What should be taught in a "Fundamentals of programming" course at university?

  - by Dervin Thunk

  I have started a new question (see here), because I think the topic is of importance in a more general form. The question is now: If you were a professor at a Computer Science Dept. in some university, what would make it into your course? This is a programming course, second term, first year computer science/computer engineering. Remember you have a limited amount of time, and students are of different levels of competence, and some may be scientists, but some will also go on to be programmers in companies of different kinds. You have to cater to all. Bonus: What language? (Although see this question for my current thoughts about this...) Maybe you want to attach a course outline from some university? See here for an even more general question about this. Answer: I can't really summarize this post... I guess it was too subjective. However, it looks like we have to cover the history of computing up to a certain extent, computer architecture (memory, registers, whatever), C, and finally some basic algos and data structures in a problem solving fashion. This will be the bare bones of the course. Thanks all. I will accept the most voted up answer to close the thread, as it should be done.

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• How to detect a gamepad button press on OSX 10.5 and higher?

  - by Steph Thirion

  How do I detect a button press on a USB gamepad on OSX 10.5 and higher? I can't wrap my head around the ridiculously complex HID Manager (even though apparently it was simplified with 10.5), and the code samples at Apple have thousands of lines of code that would take days to understand and isolate what I need, so I'd appreciate if someone posts a simple, and fully coded solution for this isolated problem. EDIT: so far all answers are links to source code or semi obscure libraries for all kinds of HID devices, which will require more research time than what I'd like to invest on this. I am starting a bounty to get an actual snippet of code that solves this simple problem (using an external library or not). EDIT POS BOUNTY: thanks to all for you help; but unfortunately the answer that has been automatically selected by the system is not working for me, can't figure out why; and the author has not yet replied to my comments. Any insight would be appreciated, but until a fix is found, anyone looking for resources on this topic should take this answer with a pinch of salt.

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• Algorithm Question

  - by Ravi

  Hi, I am trying to find a O (n) algorithm for this problem but unable to do so even after spending 3 - 4 hours. The brute force method times out (O (n^2)). I am confused as to how to do it ? Does the solution requires dynamic programming solution ? http://acm.timus.ru/problem.aspx?space=1&num=1794 In short the problem is this: There are some students sitting in circle and each one of them has its own choice as to when he wants to be asked a question from a teacher. The teacher will ask the questions in clockwise order only. For example: 5 3 3 1 5 5 This means that there are 5 students and : 1st student wants to go third 2nd student wants to go third 3rd student wants to go first 4th student wants to go fifth 5th student wants to go fifth. The question is as to where should teacher start asking questions so that maximum number of students will get the turn as they want. For this particular example, the answer is 5 because 3 3 1 5 5 2 3 4 5 1 You can see that by starting at fifth student as 1st, 2 students (3 and 5) are getting the choices as they wanted. For this example the answer is 12th student : 12 5 1 2 3 6 3 8 4 10 3 12 7 because 5 1 2 3 6 3 8 4 10 3 12 7 2 3 4 5 6 7 8 9 10 11 12 1 four students get their choices fulfilled. Thanks Ravi

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