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matlabmatrixmatrix-multiplication

unable to multiply matrix in matlab

Good day!

I am trying to multiply two matrices those are:

z = [64 x 1] ; with complex attribute.

top = [32 x 64]

both of the matrices class are double but when I tried to run the program I got an error at the last line

Matrix dimensions must agree.

here is the code:

clear all; clc;
load('eeg.mat'); 

load('top.mat');

N = 64;
M = 32;


Psi = dftmtx(N);
z = Psi * VarName1;
y = z * top;

the output that I want is [32 x 1]

Solution

  • You seem to have the product y = z * top where size(z) == [64, 1] and size(top) == [32, 64]. The sizes of these two matrices are incompatible to be multiplied in this order, as the "inner" dimensions must agree, but in your case 1 ~= 32 (see https://en.wikipedia.org/wiki/Matrix_multiplication#Definition). What you probably want is

    y = top * z