How to do this more efficiently
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Hello,
I have this piece of code in MATLAB:
for kk=0:N-1
for mm=0:N-1
for pp=1:Np
for qq=1:Np
if ((kk*Ts+tau(pp)))<=(mm*Ts+tau(qq))) && ((kk+1)*Ts+tau(pp))>(mm*Ts+tau(qq)))
thetaSR=(((kk+1)*Ts+tau(pp)))-((mm*Ts+tau(qq))));
F_SR_MR(kk+1,mm+1)=F_SR_MR(kk+1,mm+1)+conj(H(pp))*H(qq)*(thetaSR*exp(1i*pi*fc**thetaSR)*sinc(fc*thetaSR));
end
which obviously is not very efficient. How can I re-write it more efficiently?
Thanks
6 commentaires
the cyclist
le 25 Mai 2014
Do you have a reference (e.g. an image you can post) that shows the mathematical formula you are trying to replicate? It might be easier to build the code directly from that rather than optimizing yours.
Réponse acceptée
Roger Stafford
le 26 Mai 2014
It isn't necessary to do the inequality test for every possible pair of kk and mm values. Since kk and mm are integers and Ts must surely be a positive number, your pair of inequalities is logically equivalent to
kk-mm == d
where d = floor((tau(qq)-tau(pp))/Ts). Therefore you can simply add the appropriate vectors along corresponding diagonals of F. For large N, doing it this way should save quite a bit of computation time.
F=zeros(N);
for pp=1:Np
for qq=1:Np
d = floor((tau(qq)-tau(pp))/Ts);
kk = max(d,0):min(N-1,N-1+d);
mm = kk-d;
theta=(d+1)*Ts-(tau(qq)-tau(pp));
ix = d+1+(N+1)*mm;
F(ix) = F(ix)+conj(H(pp))*H(qq)*theta.*exp(1i*pi*fc*theta).*sinc(fc*theta);
end
end
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the cyclist
le 24 Mai 2014
Especially if N is large, you might get a huge speedup if you preallocate the memory for F_SR_MR. Put the line
F_SR_MR = zeros(N,N);
ahead of the loops.
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