http://www.mapleprimes.com/posts/42871-Matrix-Construction-Functions-Seem-Very-Slow en-us 2026 Maplesoft, A Division of Waterloo Maple Inc. Maplesoft Document System Wed, 10 Jun 2026 17:15:14 GMT Wed, 10 Jun 2026 17:15:14 GMT The latest comments added to the Post, Matrix Construction Functions Seem Very Slow http://www.mapleprimes.com/images/mapleprimeswhite.jpg http://www.mapleprimes.com/posts/42871-Matrix-Construction-Functions-Seem-Very-Slow http://www.mapleprimes.com/posts/42871-Matrix-Construction-Functions-Seem-Very-Slow?ref=Feed:MaplePrimes:Matrix Construction Functions Seem Very Slow:Comments#comment79878 There are several ways to do stacking and augmenting of Matrices and Vectors, some of which might depend on the type of data. If you could supply some (small, but fully detailed) examples of what you are trying to accomplish then it would be easier to make suggestions as to efficient ways to do it. Another useful piece of information is whether you would be content with a result that contained only (possibly complex) floating-point data. Thanks very much, Dave Linder Team Lead, Mathematical Software, Maplesoft, Inc. The latest comments added to the Post, Matrix Construction Functions Seem Very Slow 79878 Thu, 11 May 2006 01:33:38 Z Dave L Dave L http://www.mapleprimes.com/posts/42871-Matrix-Construction-Functions-Seem-Very-Slow?ref=Feed:MaplePrimes:Matrix Construction Functions Seem Very Slow:Comments#comment79877 The Matrix constructor is known to be slow. In this case it creates a rather expensive initialization procedure which is called for each entry of the result. You can see what I mean in the following example: A := Matrix([[1,2],[3,4]]); B := Matrix([[5,6],[7,8]]); trace(Matrix); Matrix([A,B]); If you look closely at that initializer, you will see that it evaluates the submatrices. This happens for each index (i,j) in the result. The latest comments added to the Post, Matrix Construction Functions Seem Very Slow 79877 Thu, 11 May 2006 02:31:31 Z roman_pearce roman_pearce http://www.mapleprimes.com/posts/42871-Matrix-Construction-Functions-Seem-Very-Slow?ref=Feed:MaplePrimes:Matrix Construction Functions Seem Very Slow:Comments#comment86515 First of all thank you both very much for your input. Basically what I am trying to do is to combine four square matrices, usually, of order ~ 256x256 into one ~512x512 matrix (although sometimes I just need to stack two of these together, but in general I do the first thing). The reason for doing this is that I have written an optical modelling code that requires me to construct the initial smaller matrices which represent individual electric and magnetic field boundary conditions. I then want to do simple matrix operations on the resulting matrices, nothing particularly extreme just simple addition and multiplication as well as solving Ax=b using LinearSolve, in order to match these conditions. I have tried writing simple for loops that copy the individual [i,j] entries across into a pre-initialized larger matrix, although this is slightly quicker it still seems to take an inordinate amount of time. If there is a better way of combining them or if my calculations can be done without combining the matrices at all then that would certainly speed things up. My result would indeed only contain floating point numbers although as I mentioned they would definitely be complex and often beyond hardware precision and exponent. Thank you again, Martyn The latest comments added to the Post, Matrix Construction Functions Seem Very Slow 86515 Thu, 11 May 2006 14:05:57 Z py9mrg py9mrg http://www.mapleprimes.com/posts/42871-Matrix-Construction-Functions-Seem-Very-Slow?ref=Feed:MaplePrimes:Matrix Construction Functions Seem Very Slow:Comments#comment90676 You can try the following: <tt> My := Matrix(512,512): My[1..256,1..256] := M1: My[1..256,257..512] := M2: My[257..512,1..256] := M3: My[257..512,257..512] := M4: </tt> This creates the target matrix and then just copies the entries over without evaluation. Here is a complete test case: Create test matrices: <tt> M1 := LinearAlgebra:-RandomMatrix(256,256); M2 := LinearAlgebra:-RandomMatrix(256,256); M3 := LinearAlgebra:-RandomMatrix(256,256); M4 := LinearAlgebra:-RandomMatrix(256,256); </tt> This takes about 40 seconds on my computer: <tt> st:=time(): Mx := &lt;&lt;M1|M2&gt;,&lt;M3|M4&gt;&gt;; time()-st; </tt> This takes less than a second on my computer: <tt> st := time(): My := Matrix(512,512): My[1..256,1..256] := M1: My[1..256,257..512] := M2: My[257..512,1..256] := M3: My[257..512,257..512] := M4: time()-st; </tt> Check that both techniques produce the same matrix: <tt> LinearAlgebra:-Norm(Mx-My); </tt> Jan Bakus Applications Engineer, Maplesoft The latest comments added to the Post, Matrix Construction Functions Seem Very Slow 90676 Thu, 11 May 2006 18:56:10 Z jan jan http://www.mapleprimes.com/posts/42871-Matrix-Construction-Functions-Seem-Very-Slow?ref=Feed:MaplePrimes:Matrix Construction Functions Seem Very Slow:Comments#comment90677 Thank you very very much for that. It has speeded up those processes incredibly, and as a result my model now runs much much much faster than it did! Thank you again. Martyn The latest comments added to the Post, Matrix Construction Functions Seem Very Slow 90677 Thu, 11 May 2006 21:53:49 Z py9mrg py9mrg