Thread: Help on Improving performance for MATLAB function

Im trying to make my function run faster and I was wondering if anyone can help me. I'm trying to calculate the following equation :
ImageShack - Image Hosting :: 29384513.jpg
where N and M are inputs. Basically i need to caluclate that sum for all values of m.
This is my current code:

function [e] = new5(M,N)

tic;

k=3;
n=(1:1:N);
d=zeros(1,M-1);
b=zeros(1,M-1);

for m=1:1:M-1;
d=m./M;
b=cos((n.^k)*d);
e(m)=(sum(b)/sqrt(N));
end

hold on
%plot histogram of data
hist(e,100);figure(gcf);
hold off
toc;

Any ideas?

Originally Posted by thankarathan

Im trying to make my function run faster and I was wondering if anyone can help me. I'm trying to calculate the following equation :
ImageShack - Image Hosting :: 29384513.jpg
where N and M are inputs. Basically i need to caluclate that sum for all values of m.
This is my current code:

function [e] = new5(M,N)

tic;

k=3;
n=(1:1:N);
d=zeros(1,M-1);
b=zeros(1,M-1);

for m=1:1:M-1;
d=m./M;
b=cos((n.^k)*d);
e(m)=(sum(b)/sqrt(N));
end

hold on
%plot histogram of data
hist(e,100);figure(gcf);
hold off
toc;

Any ideas?

Code:

N=3;M=4;
 

tic;
 

k=3;
n=(1:1:N);
d=zeros(1,M-1);
b=zeros(1,M-1);
 

n=1:N;
m=1:M-1;
 
d=m/M;
theta=n'.^k*d;
b=cos(theta);
e=sum(b)/sqrt(N);
 
hold on

plot histogram of data
hist(e,100);figure(gcf);
hold off

toc

CB

Thank you for your reply. Your code does indeed work a lot faster, however since I;m taking large values of N and M, I get an "out of memory" error for values of M,N> 5000

Originally Posted by thankarathan

Thank you for your reply. Your code does indeed work a lot faster, however since I;m taking large values of N and M, I get an "out of memory" error for values of M,N> 5000

Then you will have to segment the calculation over sub-blocks of M or N and loop over the blocks.

Something like (this is untested by the way, so no guarantees):

Code:

N=3;M=4;
 

tic;
 

k=3;

BlockLen=1000;
e=zeros(1,M-1);

m=1:M-1;

for idx=1:1000:N

  n=(idx:min(N,idx+BlockLen-1));
 
  d=m/M;
  theta=n'.^k*d;
  b=cos(theta);
  e=e+sum(b)/sqrt(N);

end
 
hold on

plot histogram of data
hist(e,100);figure(gcf);
hold off

toc

CB