how to save values for changing number of columns using "for loop "

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Khan
Khan 2021-6-23
评论： Khan 2021-6-23
I want to run a simple code, but i am unable to get the results correctly. A simple code is wriiten below, I am changing number of columns of one parameter. for that i want to save value of X_telda (10), X_telda(50) and X_telda(100) separately. U and X are given matrices.
for r=[10 50 100];
X_telda=(U(:,1:r)*(U(:,1:r)'*X));
end
thank you

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KSSV
KSSV 2021-6-23
r=[10 50 100] ;
n = length(r) ;
X_telda = cell(n,1) ;
for i = 1:n
X_telda{i} = (U(:,1:r(i))*(U(:,1:r(i))'*X));
end
X_telda is a cell, you can access it using X_telda{1},..etc

更多回答（1 个）

Walter Roberson
Walter Roberson 2021-6-23
We do not know the size of U. Call it N x M
U(:,1:r) is an N x r matrix
U(:,1:r)' is an r x N matrix.
X we do not know the size of, but in order to * it by an r x N matrix, we can tell that X must be N x something. Call it N x P
So U(:,1:r)' * X would be r x N * N x P giving r x P
U(:,1:r) * that would be N x r * r * P, so the overall operation would give N x P .
To put it another way, X_telda is size(U,1) by size(X,2)
Your code does not have any obvious problems, other than the fact that you are not storing the results X_telda before overwriting them in the next loop. But how do you want the multiple outputs represented?
Well, one way would be to use:
rvals = [10 50 100];
numr = length(rvals);
X_telda = zeros(size(U,1), size(X,2), numr);
for ridx = 1 : numr
r = rvals(ridx);
X_telda(:,:,ridx) = U(:,1:r)*(U(:,1:r)'*X));
end

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