# How I compute multiple sum in matlab for 4D matrix?

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Mehdi on 11 Sep 2018
Commented: Mehdi on 11 Sep 2018
How I compute multiple sum in matlab for 4D matrices as below? U and V are 4D matrices.
Mehdi on 11 Sep 2018
Edited: Mehdi on 11 Sep 2018
As I said I have many similar expressions like that and it seems your method is not applicable for more expressions. I am searching a similar command like add in Maple.
Matt J on 11 Sep 2018
Edited: Matt J on 11 Sep 2018
If they are "similar", my method - which is to use the sum command - is applicable. Have you read the documentation on sum()? It is the best analogue of add that you will find in Matlab.

Matt J on 11 Sep 2018
Edited: Matt J on 11 Sep 2018
Notice that the only indices shared between U and V are j and q. Therefore, you can minimize multiplication operations as follows,
partialU=sum(sum(U,4),1); %sum over i and r
partialV=sum(sum(V,4),1); %sum over k and s
A=sum(partialU(:).*partialV(:)); %sum over j and q
Matt J on 11 Sep 2018
Edited: Matt J on 11 Sep 2018
You should edit your original post with this new equation and information about q_r and q_s. The new expression is rather unclear. You have the symbol q being used for two different things, both as a symbolic variable and as an index of summation.
Mehdi on 11 Sep 2018

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