matrix

Why is MATLAB so fast in matrix multiplication?

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I am making some benchmarks with CUDA, C++, C#, Java, and using MATLAB for verification and matrix generation. When I perform matrix multiplication with MATLAB, 2048×2048 and even bigger matrices are almost instantly multiplied. 1024×1024 2048×2048 4096×4096 ——— ——— ——— CUDA C (ms) 43.11 391.05 3407.99 C++ (ms) 6137.10 64369.29 551390.93 C# (ms) 10509.00 300684.00 … Read more

Transposing a 2D-array in JavaScript

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I’ve got an array of arrays, something like: [ [1,2,3], [1,2,3], [1,2,3], ] I would like to transpose it to get the following array: [ [1,1,1], [2,2,2], [3,3,3], ] It’s not difficult to programmatically do so using loops: function transposeArray(array, arrayLength){ var newArray = []; for(var i = 0; i < array.length; i++){ newArray.push([]); }; … Read more

What are the most widely used C++ vector/matrix math/linear algebra libraries, and their cost and benefit tradeoffs? [closed]

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Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers. Want to improve this question? Update the question so it’s on-topic for Stack Overflow. Closed 4 years ago. Improve this question It seems that many projects slowly come upon a need to do matrix math, and fall into the trap … Read more

How do you rotate a two dimensional array?

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Inspired by Raymond Chen’s post, say you have a 4×4 two dimensional array, write a function that rotates it 90 degrees. Raymond links to a solution in pseudo code, but I’d like to see some real world stuff. [1][2][3][4] [5][6][7][8] [9][0][1][2] [3][4][5][6] Becomes: [3][9][5][1] [4][0][6][2] [5][1][7][3] [6][2][8][4] Update: Nick’s answer is the most straightforward, but … Read more

How can I index a MATLAB array returned by a function without first assigning it to a local variable?

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For example, if I want to read the middle value from magic(5), I can do so like this: M = magic(5); value = M(3,3); to get value == 13. I’d like to be able to do something like one of these: value = magic(5)(3,3); value = (magic(5))(3,3); to dispense with the intermediate variable. However, MATLAB … Read more

Difference between numpy.array shape (R, 1) and (R,)

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In numpy, some of the operations return in shape (R, 1) but some return (R,). This will make matrix multiplication more tedious since explicit reshape is required. For example, given a matrix M, if we want to do numpy.dot(M[:,0], numpy.ones((1, R))) where R is the number of rows (of course, the same issue also occurs … Read more