Fast Element-Wise power

Hello all,

I am trying to optimize some code that contains element wise calculations with rather large matrices. I have already shaved off about 50% with things like the bsxfun (which in my case works wonders). But now I am stuck at an operation where a simple line of code value=matrix.^3 takes up most of the runtime of the script. is there any way to perform this element-wise calculation faster?

Best regards

[Thomas Bauer]

Hello, i think i just answered my own question. Appearently using

value=matrix.*matrix.*matrix

runs significantly faster.

BTW i also figured out bsxfun was NOT the reason for my faster running script. It actually was the termination of several operations by precalculating another variable.

Answer 1

[KL]

   a=1:10000000;
  b=repmat(3,size(a));
  tic
  c1=a.^b;
  toc
  tic
  c2=a.^3;
  toc
  tic
  c3=a.*a.*a;
  toc

And then the results are,

 Elapsed time is 0.118509 seconds.
 Elapsed time is 0.129281 seconds.
 Elapsed time is 0.006726 seconds.

[Thomas Bauer]

Thank you for this example!

[Johannes Kalliauer]

sometimes if you have small integers you can speed it up by useing integers

  a=randi([0,6],1,10000000);
  b=repmat(3,size(a));
  int8a=uint8(a);
  
  tic
  c1=a.^b;
  toc
  tic
  c2=a.^3;
  toc
  tic
  c3=a.*a.*a;
  toc
  tic
  c4=int8a.*int8a.*int8a;
  toc

And then the results are,

Elapsed time is 0.199174 seconds.
Elapsed time is 0.153210 seconds.
Elapsed time is 0.014326 seconds.
Elapsed time is 0.002569 seconds.