CODEWITHSUNDEEP
matlabvectorization
CirugiaoM
CirugiaoM

Reputation: 35

Vectorization for loop

I am trying to vectorize this for loop. Any idea?

D = 1x8851;

for k = 1:length(D)-1

    P(k) = ((D(k)<=0)&&(D(k+1)>=0))||((D(k)>=0)&&(D(k+1))<0);

 end

Upvotes: 0

Views: 43

Answers (1)

Cris Luengo
Cris Luengo

Reputation: 60504

For two things having different signs, it means that their product is negative:

P(k) = ((D(k)<=0)&&(D(k+1)>=0))||((D(k)>=0)&&(D(k+1))<0);

is the same as:

P(k) = ( D(k) * D(k+1) ) <= 0;

This is simple to vectorize by simply converting operations to element-wise operations:

P = ( D(1:end-1) .* D(2:end) ) <= 0;

The original construct can be vectorized in the same way, with & and | being the element-wise counterparts to && and ||:

P = ((D(1:end-1)<=0)&(D(2:end)>=0))|((D(1:end-1)>=0)&(D(2:end))<0);

However, the shorter expression requires fewer intermediate matrices and fewer operations, and therefore will be faster.

Upvotes: 3

Related Questions