subrutine to multiplication multidimensional matrix

Can you tell me a subrutine to multiplication multidimensional matrix in Matlab?

thanks

[Andrei Bobrov]

Please give example

Answer 1

[Andrei Bobrov]

use bsxfun

ADDED on agustin darrosa's comment [EDIT] ;)

if numel(a) == numel(b)
    c1 = a - permute(b,[2 1 3 4]);
    c2 = permute(a,[2 1 3 4]) - b;
end

[Andrei Bobrov]

comment by agustin darrosa

But there is a problem, for example:

a is a multidimensional matrix with dimensions 2*3*2*2 and b is other multidimensional matrix with dimensions 3*2*2*2

iF you use

c = bsxfun(@minus, a, b)

matlab says:

*Error using ==> bsxfun Non-singleton dimensions of the two input arrays must match each other.*

But this multiplication is correct

any solution??

thanks

[Jan]

How do you know that "the multiplication" is "correct". Please define the expected result, because it cannot be guesses reliably.

[agustin darrosa]

I saw this multiplication in an example:

>> a=[ 1 3 5; 2 4 6]; >> a(:,:,1,2)=[ 13 15 17; 14 16 18]; >> a(:,:,2,1)=[ 7 9 11; 8 10 12] >> a(:,:,2,2)=[ 19 21 23; 20 22 24];

>> b=[ 24 21; 23 20; 22 19]; >> b(:,:,1,2)=[ 12 9; 11 8; 10 7]; >> b(:,:,2,1)=[ 18 15; 17 14; 16 13]; >> b(:,:,2,2)=[ 6 3; 5 2; 4 1]; >> I want multiplicate a and b

Thanks for answer

[Andrei Bobrov]

see ADDED part in my answer

[Jan]

"Multiplication" does not really remind me to the "-" operator. Did I loss the point?

[agustin darrosa]

i don´t understand you

sorry

[Jan]

@agustin: Do you mean Andrei or me? I think the main problem is, that we do not understand you. I still do not know what you expect as results.

[agustin darrosa]

OK, sorry I am spanish and my english is bad

I want to know how to multiply two multidimensional arrays in matlab

[Jan]

@agustin: Welcome in the forum! Here are a lot of non-native speakers and asking questions for clarifications is a usual process for finding solutions.

How do you define the multiplikation of multi-dimensional arrays? This is not a standard procedure in a mathematical sense, so we have to know, what you want as result.

[agustin darrosa]

I just want to see the result of the multiplication of matrices

Let a and b multidimensional array. I want to see the resulting c

c=a*b

I hope I explained correctly

thanks

[Andrei Bobrov]

Comment by agustin darrosa

Thanks andrei but i have this error:

1. First i define the matrixs a and b

2. then I insert

if numel(a) == numel(b):

c = a - permute(b,[2 1 3 4]);

or

c = permute(a,[2 1 3 4]) - b; ??? if numel(a) == numel(b): | Error: Expression or statement is incomplete or incorrect.

but i have this problem and i don´t know why

Answer 2

[James Tursa]

You haven't given an example so we don't really know what you want yet. Maybe it is this, which does a matrix multiply on the first two dimensions:

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

Answer 3

[Jan]

A = rand(2,3,2,2);
B = rand(3,2,2,2);

% A simple loop:
R = zeros(2,2,2,2);
for i1 = 1:2
  for i2 = 1:2
    R(:, :, i1, i2) = A(:, :, i1, i2) * B(:, :, i1, i2);
  end
end

Is this what you want? If so, note that this is actually a list of DOT products only. Then reshape B to a [3 x 8] array, A to a [8 x 3] (which needs a permute(A, [1,3,4,2]) also) and multiply these matrices. Finally a reshaping give the same R.

Unfortunately I do not dare to post the code, because I do not have Matlab for testing at the moment.

Answer 4

[agustin darrosa]

thanks you!!!