diagproduct.m

来自「人工神经网络的源码编程」· M 代码 · 共 35 行

function d = diagProduct(X, Y)
%  d = diagProduct(X, Y)
%
%  Outputs the diagonal of the product of X and Y.
%  Faster than diag(X*Y).
%
%  Inputs
%
%    X    matrix (m-by-n)
%    Y    matrix (n-by-m)
%
%  Output
%    d    vector (m-by-1)

[m,n] = size(X);
[p,q] = size(Y);

if m ~= q | n ~= p
  error('diagProduct: bad dimensions')
end

% P - a column vector of the rows of X
P = X';
P = P(:);

% Q - a column vector of the columns of Y
Q = Y(:);

% Z - an [n,m] matrix containing the components of P.*Q
Z = zeros(n,m);
Z(:) = P .* Q;

% d - the answer is the sum of the columns of Z
d = colSum(Z)';