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From: Vihar on 8 Dec 2009 14:22
Hello,

I've been trying to perform a 3D matrix multiplication and have not been successful. My two matrices are of size m x n x p and I want to be able to carry out A*B in 3 dimensions. I've spent a few hours on the boards here searching for some help but have failed to find anything, so your help will be greatly appreciated.

Thanks
From: dpb on 8 Dec 2009 14:34
Vihar wrote:
> Hello,
>
> I've been trying to perform a 3D matrix multiplication and have not
> been successful. My two matrices are of size m x n x p and I want to
> be able to carry out A*B in 3 dimensions. I've spent a few hours on
> the boards here searching for some help but have failed to find
> anything, so your help will be greatly appreciated.

You don't say what your definition of the result should be -- one
surmise would be --

>>
>> a=rand(2,3,2); % get some data to play with
>> b=rand(3,2,2);
>> c=zeros(size(a,1),size(b,2),size(a,3); % preallocate result
>> for i=1:size(a,3),c(:,:,i)=a(:,:,i)*b(:,:,i);end

--
From: James Tursa on 8 Dec 2009 15:54
dpb <none(a)non.net> wrote in message <hfm9p3$mbh$1(a)news.eternal-september.org>...
> Vihar wrote:
> > Hello,
> >
> > I've been trying to perform a 3D matrix multiplication and have not
> > been successful. My two matrices are of size m x n x p and I want to
> > be able to carry out A*B in 3 dimensions. I've spent a few hours on
> > the boards here searching for some help but have failed to find
> > anything, so your help will be greatly appreciated.
>
> You don't say what your definition of the result should be -- one
> surmise would be --
>
> >>
> >> a=rand(2,3,2); % get some data to play with
> >> b=rand(3,2,2);
> >> c=zeros(size(a,1),size(b,2),size(a,3); % preallocate result
> >> for i=1:size(a,3),c(:,:,i)=a(:,:,i)*b(:,:,i);end

For this result you can use my MTIMESX submission in the FEX:

http://www.mathworks.com/matlabcentral/fileexchange/25977-mtimesx-fast-matrix-multiply-with-multi-dimensional-support

a=rand(2,3,2); % get some data to play with
b=rand(3,2,2);
c=mtimesx(a,b); % fast result w/o loops

MTIMESX is a fast BLAS based nD matrix multiply routine.

James Tursa
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