## Multidimensional matrix multiplication

Version 1.2.0.0 (1.75 KB) by
The simple function performs fast matrix multiplication within multidimensional arrays.

Updated 19 Aug 2013

mmat(A,B) performs matrix multiplication, where the 2D matrices are part of multidimensional arrays. It is equivalent to the Matlab built in mtimes function for 2D arrays. However it naturally extends the mtimes function, where the two input arrays can have arbitrary number of extra dimensions. For example:

A = [1 2;2 1];
B = [3 4; 1 2];

mmat(A,B) == mtimes(A,B)

However A and B can be expanded along the 3rd dimension:

A = repmat([1 2; 2 1],[1 1 5]);

C = mmat(A,B) can be also performed, C will contains:
C(:,:,1) = A(:,:,1)*B;
C(:,:,2) = A(:,:,2)*B; ...

In the above example B was expanded along the singleton dimensions to match the size of A for the multiplication.

In the above examples the matrix multiplication was performed along the first two dimensions of A and B. However when called:
mmat(A,B,dim)
then dim selects two dimensions from A and B along which the matrix multiplication should be performed.

For example:
dim = [1 2] - default value
dim = [2 3] - C(ii,:,:) = A(ii,:,:) * B(ii,:,:);

This function contains only simple Matlab script without for loops!
Thus it is clean, fast and no compiling needed!

Enjoy!

### Cite As

Sandor Toth (2023). Multidimensional matrix multiplication (https://www.mathworks.com/matlabcentral/fileexchange/41663-multidimensional-matrix-multiplication), MATLAB Central File Exchange. Retrieved .

##### MATLAB Release Compatibility
Created with R2012b
Compatible with any release
##### Platform Compatibility
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Version Published Release Notes
1.2.0.0

Line 54/55 are changed, to fix a bug that appears when dim is not the default [1 2] value.

1.1.0.0

Corrected a small bug in the code and refreshed the file description.

1.0.0.0