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better method for evaluating matrix

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JaeSung Choi
JaeSung Choi 2017-11-21
编辑： Stephen23 2017-11-21
For given vector such as following, I want to make square matrix s such that
%constant, original form
N = 500;
x = 2*pi*linspace(0,1,N);
for i = 1:N
for j = 1:N
s(i,j) = sin(x(i)-x(j))
end
end
But it was too slow, so recently I edited it to following, but it's still too slow!!
Can anybody please help me??
%constant
N = 500;
x = 2*pi*linspace(0,1,N);
for i = 1: N;
s(:,i) = x-x(i);
end
s=sin(s);

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采纳的回答

Stephen23
Stephen23 2017-11-21
编辑：Stephen23 2017-11-21
You really need to learn how to write vectorized code. Solving every task using lots of ugly loops is not an efficient way to write MATLAB code. Try this:
N = 500;
vec = 2*pi*linspace(0,1,N);
mat = sin(bsxfun(@minus,vec(:),vec))

更多回答（1 个）

Andrei Bobrov
Andrei Bobrov 2017-11-21
编辑：Andrei Bobrov 2017-11-21
N = 500;
x = 2*pi*linspace(0,1,N);
s = sin(x(:)' - x(:));
for old versions of MATLAB:
s = sin( bsxfun(@minus, x(:)',x(:)) );
  1 个评论
Stephen23
Stephen23 2017-11-21
编辑：Stephen23 2017-11-21
Note that the output is transposed compared to the code given in the question.

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