I didn't understand how put the inputs in tprod function

Question

Francesco 2011-8-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/14046-i-didn-t-understand-how-put-the-inputs-in-tprod-function

How have I to put the input in tprod to have the same result of the code that follows?

a=rand(3,4,5);
b=rand(4,6);
for i=1:5
       c(:,i,:)=a(:,:,i)*b;
end

[edit: matrix dimension corrected]

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Answer 1

Fangjun Jiang 2011-8-19

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https://ww2.mathworks.cn/matlabcentral/answers/14046-i-didn-t-understand-how-put-the-inputs-in-tprod-function#answer_19207

a=rand(3,4,5);
b=rand(3,4);
c=zeros(size(a));
for i=1:5
       c(:,:,i)=a(:,:,i).*b;
end

Or do you mean this link? There is a 3-D example there. http://www.mathworks.com/matlabcentral/fileexchange/16275-tprod-arbitary-tensor-products-between-n-d-arrays/content/tprod.m

Okay, I tried, it should be like below. The original tprod.m does contain incorrect examples.

%%Your code
a=rand(3,4,5);
b=rand(4,6);
for i=1:5
       c(:,i,:)=a(:,:,i)*b;
end
% use tprod
Z=tprod(a,[1 -1 2],b,[-1 3]);
err=abs(Z-c);
err=sum(err(:))
err =
       0

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Fangjun Jiang 2011-8-20

That is the problem! You need to at least provide some explanation about tprod. It's not a MATLAB function anywhere. Do you mean this?

http://www.mathworks.com/matlabcentral/fileexchange/16275

Francesco 2011-8-20

Yes, I meant right it.

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Answer 2

Walter Roberson 2011-8-19

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https://ww2.mathworks.cn/matlabcentral/answers/14046-i-didn-t-understand-how-put-the-inputs-in-tprod-function#answer_19279

What is "tprod" ? It does not seem to be indexed on the MATHWORKS web site.

Your code produces an error, as at each step you are attempting to do a matrix multiplication of a 3 x 4 matrix, by a 3 x 4 matrix. Either you need to use .* to do element-by-element multiplication, or you need to change your formula.

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Francesco 2011-8-20

tprod is a function to multiply n-dimensional arrays (http://www.mathworks.com/matlabcentral/fileexchange/16275-tprod-arbitary-tensor-products-between-n-d-arrays)

About the dimensions: you're right, I corrected them right now, thanks.

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