Efficient way to multiply an cell matrix with a scaler?
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Mohammod Minhajur Rahman
on 24 Nov 2018
Commented: Guillaume
on 27 Nov 2018
Hi,
I have a for loop that multiplies a cell matrix with a scaler component. The size of K11{1,i} is never too big (maximum 50 by 50 matrix) and its a full matrix. What takes time is that sometimes the maximum value of "i" can go up to 10000 or more and I have to do it for many analysis. It would be very helpful if you could suggest a way to compute it faster by vectorizing the loop or any other way.
nonZeroDel = nnz(del);
delNonZero = nonzeros(del);
for i = 1:nonZeroDel
KE = KE + K11{1,i}*delNonZero(i);
end
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Accepted Answer
Guillaume
on 24 Nov 2018
Edited: Guillaume
on 25 Nov 2018
Since for your summation to succeed all the arrays in K11 must be the same size, convert that cell array to a 3D matrix. It will be a lot more efficient.
K11 = cat(3, K11{:});
delNonZero = permute(nonzeros(del), [3 2 1]); %move the non-zeros in the 3rd dimension
KE = sum(K11 .* delNonZero, 3);
4 Comments
Guillaume
on 27 Nov 2018
Well, I don't know how you created that K11, but it shouldn't be a cell array in the first place. It should have been created as a 3D matrix from the beginning. Cell arrays are slower than matrices, often by a lot (as was your original code). In my answer, the slowest part will be the conversion from cell to matrix.
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