inv(A) versus /A. Which of the two is the correct one

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ektor 2015-2-12

评论： Stephen23 2015-2-13

Hi all,

Let B be a n by 2 matrix and A is a 2 by 2 positive definite matrix. Which of the following two is correct

 for i=1:n
 B(i,:)*inv(A)*B(i,:)';
 end

 for i=1:n
 (B(i,:)/A)*B(i,:)';
 end

Best, Stef

Stephen23 2015-2-13

Don't use a loop, learn to vectorize your code. Matt J's answer shows this.

Matt J 2015-2-12

Both are equivalent. For large matrices the 2nd would be more efficient.

Further efficiency would be gained by vectorizing. The whole loop is just,

sum( (B/A).*B, 2)

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