How to vectorize a for-loop?
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Hello!
I would appreaciate any help vectorizing the for loop below. The problem i cannot solve is how to take out the constants from wdrive and multiply it with the rest, according to the loop below. I want to become better at vectorizing my MATLAB code so I would really appreciate any help! Thanks alot!
%S and R are square matrices (404*404).
%fc is a column vector
wdrive=0:1:800;
a2=zeros(2*dofs,(length(wdrive)));
b2=zeros(2*dofs,(length(wdrive)));
Amp=zeros(1,length(wdrive));
SRS=S*(R\S);
SRfc=S*(R\fc);
for i=1:length(wdrive)
a2(:,i)=(wdrive(i)^2*SRS+R)\(fs-wdrive(i)*SRfc);
b2(:,i)=(R)\(fc+wdrive(i)*S*a2(:,i));
Amp(i)=sqrt(a2(dofs-1,i)^2+b2(dofs-1,i)^2);
end
Accepted Answer
Matt J
on 18 May 2013
Edited: Matt J
on 18 May 2013
I don't think you can vectorize everything, but you can cut down on the operations done inside the loop,
Rfc=R\fc;
SRS=S*(R\S);
SRfc=S*(Rfc);
rhs=bsxfun(@minus,fs,SRfc*wdrive);
for i=1:length(wdrive)
a2(:,i)=(wdrive(i)^2*SRS+R)\rhs(:,i);
end
b2=Rfc+R\S*bsxfun(@times, wdrive, a2);
Amp=abs(a2(dofs-1,:)+i*b2(dofs-1,:));
5 Comments
Matt J
on 19 May 2013
The for-loop isn't slowing you down significantly. You just have a lot of matrix inversions
(wdrive(i)^2*SRS+R)
to do. There's no simplification to this that I can see, unless there is some special structure in S and R that you haven't mentioned.
More Answers (1)
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