小编Bab*_*bel的帖子

我有两种不同的方法来实现相同的东西,但我想第二种方法是最好的.但是,当第一个使用tic toc时,我得到了更好的结果.怎么会 ？

j=6;
i=j;
Savings = zeros(i,j);
Costs = magic(400);

tic;
for x=2:i
   for y=2:j
     if(x ~= y)
       Savings(x,y) = Costs(x,1) + Costs(1,y) - Costs(x,y);
     end
   end
end
first=toc;

disp(num2str(first))

Savings = zeros(i,j);

tic;
Ix=2:i; 
Iy=2:j;
I = false(i,j);
I(Ix,Iy) = bsxfun(@ne, Ix', Iy);
S = bsxfun(@plus, Costs(Ix,1), Costs(1,Iy)) - Costs(Ix,Iy);
Savings(I) = S(I(Ix,Iy));
second=toc;

temp = Savings;
disp(num2str(second))