![]() ![]() I find the products and only sum on the products that produce a real number (eg 1nannan therefore. In my nested loop format I run through every column of B for each row of A. You can observe that bsxfun is slightly faster. The basic idea of matrix multiplication is to sum the products of the rows of matrix A sza 0, sza 1 by the columns of B szb 0, szb 1, where sza 1 szb 0. Solution using bsxfun provided by : 0.683331 seconds.The first vector has to be a column vector and the second a row vector, otherwise the multiplication isnt defined. Efficient memory access patterns and multi-threading are already built in to this library. For the matrix multiply operation, MATLAB actually calls a BLAS library function (dgemm) to do the work. That will give a matrix with length (B) rows and length (A) columns. a rand (1000) arbitrary 1000x1000 matrix. Solution using indexing technique explained above : 0.734435 seconds More Answers (1) where A is a row vector and B is a column vector (you may need to transpose them to get them in this form).Solution using repmat : 0.824518 seconds.I ran three solutions 100000 times, namely, Thereby achieving the same behavior as repmat and be faster. MATLAB, start with a 46 VECTORS, MATRICES, AND LINEAR SYSTEMS CHAPTER 1. ![]() If you see closely, the expression boils down to vec1('*),:) which is again: vec1(),:) The entry c1 in Cij the ith row and jth column of C. If youre using MATLAB 6. Observe that you can write the following statement repmat(vec1,) Īs vec1('*ones(1,size(mat1,1)),:) For long vectors prior to MATLAB 6.5 (R13), this may take a significant amount of time however, making use of the acceleration technology introduced in MATLAB 6.5 (R13), this time is drastically reduced. Alternatively, you can calculate the dot product A B with the syntax dot (A,B). Matrix indexing can achieve the same behavior as repmat and be faster. The result is a 1-by-1 scalar, also called the dot product or inner product of the vectors A and B. Given a matrix A, I need to multiply with another constant vector B, N times (N > 1 million). There is an alternative to repmat that I would like you to know. Then we can do element-wise multiplication (.*) to "multiply every column of a M × N matrix by corresponding element of a vector of size N".Įdit: Just to add to the computational aspect. For example: Here we multiply a 5 by 4 matrix with 3 vectors, each is 4 by 1. But if you mean you have a matrix of vectors, and you want to multiply another matrix by each one of these vectors then one way is to use arrayfun. Rempat will replicate vec1 along the rows of mat1. I am not sure if I understood exactly what you are asking. I think this is what you want: mat1=randi(10,) ![]()
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