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• Matrix inversion in OpenCL

  - by buchtak

  Hi, I am trying to accelerate some computations using OpenCL and part of the algorithm consists of inverting a matrix. Is there any open-source library or freely available code to compute lu factorization (lapack dgetrf and dgetri) of matrix or general inversion written in OpenCL or CUDA? The matrix is real and square but doesn't have any other special properties besides that. So far, I've managed to find only basic blas matrix-vector operations implementations on gpu. The matrix is rather small, only about 60-100 rows and cols, so it could be computed faster on cpu, but it's used kinda in the middle of the algorithm, so I would have to transfer it to host, calculate the inverse, and then transfer the result back on the device where it's then used in much larger computations.

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• Stochastic calculus library in python

  - by LeMiz

  Hello, I am looking for a python library that would allow me to compute stochastic calculus stuff, like the (conditional) expectation of a random process I would define the diffusion. I had a look a at simpy (simpy.sourceforge.net), but it does not seem to cover my needs. This is for quick prototyping and experimentation. In java, I used with some success the (now inactive) http://martingale.berlios.de/Martingale.html library. The problem is not difficult in itself, but there is a lot non trivial, boilerplate things to do (efficient memory use, variable reduction techniques, and so on). Ideally, I would be able to write something like this (just illustrative): def my_diffusion(t, dt, past_values, world, **kwargs): W1, W2 = world.correlated_brownians_pair(correlation=kwargs['rho']) X = past_values[-1] sigma_1 = kwargs['sigma1'] sigma_2 = kwargs['sigma2'] dX = kwargs['mu'] * X * dt + sigma_1 * W1 * X * math.sqrt(dt) + sigma_2 * W2 * X * X * math.sqrt(dt) return X + dX X = RandomProcess(diffusion=my_diffusion, x0 = 1.0) print X.expectancy(T=252, dt = 1./252., N_simul= 50000, world=World(random_generator='sobol'), sigma1 = 0.3, sigma2 = 0.01, rho=-0.1) Does someone knows of something else than reimplementing it in numpy for example ?

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• Javas Math.sin() produces NaN all the time

  - by milan1612

  Forgive me if this is a dumb beginners problem, but I really don't get it. I have a member variable declared like so: public Double Value; When I assign 3.14159265 to Value and try to compute the sine of it, this happens: system.out.println(Value.toString()); //outputs 3.14159265 Value = Math.sin(Value); system.out.println(Value.toString()); //outputs NaN In fact, this happens with every single value I tried - even with 0! Math.sin() seems to always produce NaN as a result, regardless of the arguments value. The docs say: If the argument is NaN or an infinity, then the result is NaN. But my argument is clearly not NaN or infinity! What the heck is happening there?

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• iPhone: Howto get notified when an UIView becomes visible

  - by arne_

  Is there a way to get a notification, a callback or some other means to call a method whenever a UIView becomes visible for the user, i.e. when a UIScrollview is the superview of some UIViews, and the ViewController of such a UIView shall get notified when its view is now visible to the user? I am aware of the possible, but not so elegant solution of checking to which position the ScrollView scrolled (via UIScrollViewDelegate-methods) and compute if either one of the subviews is visible... But I'm looking for a more universal way of doing this.

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• dataset not getting all the resultant tables i.e multiple tables are not being displayed in dataset

  - by Shantanu Gupta

  How to fill multiple tables in a dataset. I m using a query that returns me four tables. At the frontend I am trying to fill all the four resultant table into dataset. Here is my Query. Query is not complete. But it is just a refrence for my Ques Select * from tblxyz compute sum(col1) suppose this query returns more than one table, I want to fill all the tables into my dataset I am filling result like this con.open(); adp.fill(dset); con.close(); Now when i checks this dataset. It shows me that it has four tables but only first table data is being displayed into it. rest 3 dont even have schema also. What i need to do to get desired output

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• Why darcs instead of git?

  - by Ctrl Alt D-1337

  Using pure functional languages can have a lot of benefits over using impure imperatives but low level systems languages will generally allow you to achieve much greater performance especially when they are imperative because it allows you to specify the exact steps in how the cpu should compute the result. If there is ever list of tools where high performance is an absolute must then I would put source version controls systems right at the top of that list and git achieves this very well but performance is not it's only advantage over many other other types of version control systems anyway. The git team are handling the unsafe c code very well and I never worry about my type system or any other features of the language it is written in so why is it that there is a lot of haskell developers that must use darcs when they will only be using the finished product?

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• Bounding Boxes for Circle and Arcs in 3D

  - by David Rutten

  Given curves of type Circle and Circular-Arc in 3D space, what is a good way to compute accurate bounding boxes (world axis aligned)? Edit: found solution for circles, still need help with Arcs. C# snippet for solving BoundingBoxes for Circles: public static BoundingBox CircleBBox(Circle circle) { Point3d O = circle.Center; Vector3d N = circle.Normal; double ax = Angle(N, new Vector3d(1,0,0)); double ay = Angle(N, new Vector3d(0,1,0)); double az = Angle(N, new Vector3d(0,0,1)); Vector3d R = new Vector3d(Math.Sin(ax), Math.Sin(ay), Math.Sin(az)); R *= circle.Radius; return new BoundingBox(O - R, O + R); } private static double Angle(Vector3d A, Vector3d B) { double dP = A * B; if (dP <= -1.0) { return Math.PI; } if (dP >= +1.0) { return 0.0; } return Math.Acos(dP); }

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• How to fill dataset when sql is returning more than one table

  - by Shantanu Gupta

  How to fill multiple tables in a dataset. I m using a query that returns me four tables. At the frontend I am trying to fill all the four resultant table into dataset. Here is my Query. Query is not complete. But it is just a refrence for my Ques Select * from tblxyz compute sum(col1) suppose this query returns more than one table, I want to fill all the tables into my dataset I am filling result like this con.open(); adp.fill(dset); con.close(); Now when i checks this dataset. It shows me that it has four tables but only first table data is being displayed into it. rest 3 dont even have schema also. What i need to do to get desired output

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• Compile time string hashing

  - by Caspin

  I have read in few different places that using c++0x's new string literals it might be possible to compute a string's hash at compile time. However, no one seems to be ready to come out and say that it will be possible or how it would be done. Is this possible? What would the operator look like? I'm particularly interested use cases like this. void foo( const std::string& value ) { switch( std::hash(value) ) { case "one"_hash: one(); break; case "two"_hash: two(); break; /*many more cases*/ default: other(); break; } } Note: the compile time hash function doesn't have to look exactly as I've written it. I did my best to guess what the final solution would look like, but meta_hash<"string"_meta>::value could also be a viable solution.

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• Pipe implementation

  - by nunos

  I am trying to implement a linux shell that supports piping. I have already done simple commands, commands running in background, redirections, but piping is still missing. I have already read about it and seen some snippets of code, but still haven't been able to sort out a working solution. What I have so far: int fd[2]; pid_t pid = fork(); if (pid == -1) return -1; if (pid == 0) { dup2(0, fd[0]); execlp("sort", "sort", NULL); } I am a novice programmer, as you can probably tell, and when I am programming something I don't know much about, this being obviously the case, I like to start with something really easy and concrete and then build from there. So, before being able to implement three and more different commands in pipeline, I would like to be able to compute "ls names.txt | sort" or something similiar, in which names.txt is a file of names alfabetically unordered. Thanks.

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• ASP.NET Hosting Options

  - by Adam Haile

  I'm not trying to start a "which language is better" argument here, so please don't go there. I typically use PHP for most of my web development (mostly because hosting is cheap), but for various reasons I'm looking to use ASP.NET for a couple new projects. But one of the major reasons I've stayed away from ASP.NET up until now is the cost. I've seen some budget hosting options, but they always seem a little sketchy to me. From what I've generally found, that's just the way the hosting scene looks for ASP.NET unless you want to go dedicated. Does anyone have any good suggestions for a solid ASP.NET host with a good feature set and reliability for my money? Also, are there any options out there along the lines of Amazon's Elastic Compute Cloud? And yes, I know... Mono. I'm talking about Windows based "grid" hosting options?

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• What are the default values for arch and code options when using nvcc?

  - by Auron

  When compiling your CUDA code, you have to select for which architecture your code is being generated. nvcc provides two parameters to specify this architecture, basically: arch specifies the virtual arquictecture, which can be compute_10, compute_11, etc. code specifies the real architecture, which can be sm_10, sm_11, etc. So a command like this: nvcc x.cu -arch=compute_13 -code=sm_13 Will generate 'cubin' code for devices with 1.3 compute capability. Please correct me if I'm wrong. Which I would like to know is which are the default values for these two parameters? Which is the default architecture that nvcc uses when no value for arch or code is specified?

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• Statistics: combinations in Python

  - by Morlock

  I need to compute combinatorials (nCr) in Python but cannot find the function to do that in 'math', 'numyp' or 'stat' libraries. Something like a function of the type: comb = calculate_combinations(n, r) I need the number of possible combinations, not the actual combinations, so itertools.combinations does not interest me. Finally, I want to avoid using factorials, as the numbers I'll be calculating the combinations for can get to big and the factorials are going to be monstruous. This seems like a REALLY easy to answer question, however I am being drowned in questions about generating all the actual combinations, which is not what I want. :) Many thanks

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• md5 hash for file without File Attributes

  - by Glennular

  Using the following code to compute MD5 hashs of files: Private _MD5Hash As String Dim md5 As New System.Security.Cryptography.MD5CryptoServiceProvider Dim md5hash() As Byte md5hash = md5.ComputeHash(Me._BinaryData) Me._MD5Hash = ByteArrayToString(md5hash) Private Function ByteArrayToString(ByVal arrInput() As Byte) As String Dim sb As New System.Text.StringBuilder(arrInput.Length * 2) For i As Integer = 0 To arrInput.Length - 1 sb.Append(arrInput(i).ToString("X2")) Next Return sb.ToString().ToLower End Function We are getting different hashes depending on the create-date and modify-date of the file. We are storing the hash and the binary file in a SQL DB. This works fine when we upload the same instance of a file. But when we save a new instance of the file from the DB (with today's date as the create/modify) on the file-system and then check the new hash versus the MD5 stored in the DB they do not match, and therefor fail a duplicate check. How can we check for a file hash excluding the file attributes? or is there a different issue here?

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• printf field width : bytes or chars?

  - by leonbloy

  The printf/fprintf/sprintf family supports a width field in its format specifier. I have a doubt for the case of (non-wide) char arrays arguments: Is the width field supposed to mean bytes or characters? What is the (correct-de facto) behaviour if the char array corresponds to (say) a raw UTF-8 string? (I know that normally I should use some wide char type, that's not the point) For example, in char s[] = "ni\xc3\xb1o"; // utf8 encoded "niño" fprintf(f,"%5s",s); Is that function supposed to try to ouput just 5 bytes (plain C chars) (and you take responsability of misalignments or other problems if two bytes results in a textual characters) ? Or is it supposed to try to compute the length of "textual characters" of the array? (decodifying it... according to the current locale?) (in the example, this would amount to find out that the string has 4 unicode chars, so it would add a space for padding).

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• How to re-use a thread in Java ?

  - by David

  I am a building a console Sudoku Solver where the main objective is raw speed. I now have a ManagerThread that starts WorkerThreads to compute the neibhbors of each cell. So one WorkerThread is started for each cell right now. How can I re-use an existing thread that has completed its work? The Thread Pool Pattern seems to be the solution, but I don't understand what to do to prevent the thread from dying once its job has been completed. ps : I do not expect to gain much performance for this particular task, just want to experiment how multi-threading works before applying it to the more complex parts of the code. Thanks

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• Passing Boost uBLAS matrices to OpenGL shader

  - by AJM

  I'm writing an OpenGL program where I compute my own matrices and pass them to shaders. I want to use Boost's uBLAS library for the matrices, but I have little idea how to get a uBLAS matrix into OpenGL's shader uniform functions. matrix<GLfloat, column_major> projection(4, 4); // Fill matrix ... GLuint projectionU = glGetUniformLocation(shaderProgram, "projection"); glUniformMatrix4fv(projectionU, 1, 0, (GLfloat *)... Um ...); Trying to cast the matrix to a GLfloat pointer causes an invalid cast error on compile.

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• x86 assembler question

  - by b-gen-jack-o-neill

  Hi, I have 2 simple, but maybe tricky questions. Let´s say I have assembler instruction: MOV EAX,[ebx+6*7] - what I am curious is, does this instruction really actually translates into opcode as it stands,so computation of code in brackets is encoded into opcode, or is this just pseudo intruction for compiler, not CPU, so that compiler before computes the value in brackets using add mul and so, store outcome in some reg and than uses MOV EAX,reg with computed value? Just to be clear, I know the output will be the same. I am interested in execution. Second is about LEA instruction. I know what it does, but I am more interested wheather its real instruction, so compiles does not further change it, just make it into opcode as it stands, or just pseudo code for compiler to, again, first compute adress and than store it.

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• How to calculate dawn / dusk times

  - by ryyst

  Hi, I'm currently using this code to calculate the sunrise / sunset times. (To be more precise, I'm looking for civil dawn / civil dusk times which are defined as the time when the sun is between 0° and -6° altitude). As a next step, I'd like to compute the dawn beginning and dusk ending times. I believe the calculations must be very similar. My idea is that if I want to calculate the dawn beginning (dusk ending) time for a place I just calculate the sunrise (sunset) times for a place 6° farther east (west). Can somebody confirm this assumption, or am I thinking wrong? Thanks for answers! -- Ry

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• LINQ and set difference

  - by Pierre

  I have two collections a and b. I would like to compute the set of items in either a or b, but not in both (a logical exclusive or). With LINQ, I can come up with this: IEnumerable<T> Delta<T>(IEnumerable<T> a, IEnumerable<T> b) { return a.Except (b).Union (b.Except (a)); } I wonder if there are other more efficient or more compact ways of producing the difference between the two collections.

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• Sum of path products in DAG

  - by Jules

  Suppose we have a DAG with edges labeled with numbers. Define the value of a path as the product of the labels. For each (source,sink)-pair I want to find the sum of the values of all the paths from source to sink. You can do this in polynomial time with dynamic programming, but there are still some choices that can be made in how you decompose the problem. In my case I have one DAG that has to be evaluated repeatedly with different labelings. My question is: for a given DAG, how can we pre-compute a good strategy for computing these values for different labelings repeatedly. It would be nice if there was an algorithm that finds an optimal way, for example a way that minimizes the number of multiplications. But perhaps this is too much to ask, I would be very happy with an algorithm that just gives a good decomposition.

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• Best similarity metric for collaborative filtering?

  - by allclaws

  I'm trying to decide on the best similarity metric for a product recommendation system using item-based collaborative filtering. This is a shopping basket scenario where ratings are binary valued - the user has either purchased an item or not - there is no explicit rating system (eg, 5-stars). Step 1 is to compute item-to-item similarity, though I want to look at incorporating more features later on. Is the Tanimoto coefficient the best way to go for binary values? Or are there other metrics that are appropriate here? Thanks.

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• Data tweaking code runs fine when executed directly - but never stops when used in trigger

  - by MBaas

  I have written some code to ensure that items on an order are all numbered (the "position number" or "item number" has been introduced only recently and we did not want to go and change all related code - as it is "asthetics only" and has no functional impact.) So, the idea is to go and check for an records that jave an itemno of NULL or 0 - and then compute one and assign it. When executing this code in a query window, it works fine. When putting it into an AFTER INSERT-trigger, it loops forever. So what is wrong here? /****** Objekt: Trigger [SetzePosNr] Skriptdatum: 02/28/2010 20:06:29 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TRIGGER [SetzePosNr] ON [dbo].[bestellpos] AFTER INSERT AS BEGIN DECLARE @idb int DECLARE @idp int DECLARE @pnr int SELECT @idp=id,@idb=id_bestellungen FROM bestellpos WHERE posnr IS NULL OR posnr=0 WHILE @idp IS NOT NULL BEGIN SELECT @pnr = 1+max(posnr) FROM bestellpos WHERE id_bestellungen = @idb print( 'idp=' + str(@idp) + ', idb=' + str(@idb) + ', posnr=' + str(@pnr)) UPDATE bestellpos SET posnr=@pnr WHERE id=@idp SELECT @idp=id,@idb=id_bestellungen FROM bestellpos WHERE posnr IS NULL OR posnr=0 END END

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• Haskell compile time function calculation

  - by egon

  I would like to precalculate values for a function at compile-time. Example (real function is more complex, didn't try compiling): base = 10 mymodulus n = n `mod` base -- or substitute with a function that takes -- too much to compute at runtime printmodules 0 = [mymodulus 0] printmodules z = (mymodulus z):(printmodules (z-1)) main = printmodules 64 I know that mymodulus n will be called only with n < 64 and I would like to precalculate mymodulus for n values of 0..64 at compile time. The reason is that mymodulus would be really expensive and will be reused multiple times.

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• Visual Studio error on valid SQL

  - by Sam

  I'm getting an annoying error in visual studio for SQL that executes fine. SELECT InvoiceLines.LineID, InvoiceLines.InvoiceID, InvoiceLines.Text, InvoiceLines.Rate, InvoiceLines.Count, InvoiceLines.Rate * InvoiceLines.Count AS LineTotal, ((InvoiceLines.Rate * InvoiceLines.Count) * (1 + Invoices.VatRate / 100)) * (1 - CAST(Invoices.Discount AS money) * InvoiceLines.ApplyDiscount / 100) AS LineTotalIncVat, InvoiceLines.ApplyDiscount FROM InvoiceLines LEFT JOIN Invoices ON Invoices.InvoiceID = InvoiceLines.InvoiceID What LineTotalIncVat is trying to do is compute the total for the invoice item while adding the vat and subtracting the discount, and yes, probably better to do this in code (would if I could) The error visual studio gives is: There was an error parsing the query [token line number =1, token line offset =14, token in error = InvoiceLines] Even though it will validate and execute without a problem in the query builder...

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