better method for evaluating matrix

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JaeSung Choi
JaeSung Choi il 21 Nov 2017
Modificato: Stephen23 il 21 Nov 2017
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);

Risposta accettata

Stephen23
Stephen23 il 21 Nov 2017
Modificato: Stephen23 il 21 Nov 2017
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))

Più risposte (1)

Andrei Bobrov
Andrei Bobrov il 21 Nov 2017
Modificato: Andrei Bobrov il 21 Nov 2017
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 Commento
Stephen23
Stephen23 il 21 Nov 2017
Modificato: Stephen23 il 21 Nov 2017
Note that the output is transposed compared to the code given in the question.

Accedi per commentare.

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