CODEWITHSUNDEEP
matlabfor-loopvectorization
MatlabDog
MatlabDog

Reputation: 41

Eliminating for loops in Matlab

Here's a simple question. The following nested for loop creates an array of sine-wave values.

N = 2^16;
for m = 1:10;
    for i = 1:N
        sine(m,i) = sin(2*pi*i./(8*2^m));
    end
end

It seems like I should be able to create this array without the use of the for loops, but I've tried various syntaxes and always get an error message. Thanks in advance for any insights.

Upvotes: 4

Views: 109

Answers (3)

Nick
Nick

Reputation: 3193

Try the following:

ii = 1:2^16;
m  = [1./(2.^(1:10))].'% transpose

prefactor = 2 * pi / 8;

sine = sin(prefactor * m * ii);

I perform a matrix multiplication A*B, in which a is a column vector size nrows, and B is a row vector size ncols, the resulting matrix will be of size nrows x ncols. Therefore m is a column vector and ii a row vector.

Upvotes: 5

MeMyselfAndI
MeMyselfAndI

Reputation: 1320

You could use bsxfun like this: 

sine = sin(bsxfun(@times, 2*pi*(1:2^16), 1./(8*2.^(1:10))' ));

Upvotes: 6

Dan
Dan

Reputation: 45741

Try using ndgrid

N=2^16;
[M, I] = ndgrid(1:10, 1:N);
sine = sin(2*pi*I./(8*2.^M));

Upvotes: 4

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