Multiply each row of a matrix by a matrix

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Sidafa 2017-1-20

评论： Matt J 2017-1-20

Say I have the following matrix

B = [1 2 3;4 5 6;7 8 9;10 11 12]

and another matrix

A = [a b c;d e f;g h i]

How do I multiply each row of matrix B by the matrix A (without using a for loop), i.e

for i = 1:4
    c(i) = B(i,:)*A*B(i,:)'
end

many thanks in advance.

James Tursa 2017-1-20

编辑：James Tursa 2017-1-20

c = sum(bsxfun(@times,B',A*B'));

or another way, but does a lot of extra work for the off-diagonals that are discarded:

c = diag(B*A*B');

Matt J 2017-1-20

No need for bsxfun, I don't think

c=sum((B*A.').*B,2);

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