How can i make comparison faster

My aim with the loop is to pick out all elements of C that are within range r of rd and range t of td (rd and td are range matrices). Then multiply the elements together and add them to a sum.

This loop is called about a million times and is relatively slow.

Does anyone have an idea of how I can increase the speed of the loop? (I have tried code generation which turned out slower, and parallelism)

for i = 1:indN

      D = C(rd(ind(i),:)<r & td(ind(i),:)<t); % Check for <r and <t
      if (isempty(D)) D=0; end    
      gSum = gSum + prod(D);
  end

Profiling gives that D=C(.. line takes 84,7% of the entire run time (the other lines in the loop next to nothing)

[Jan]

Please provide some test data. Optimizing code depends on the inputs also. E.g. it matters, if there are repetitions in ind, or if C is a [1e7 x 1e2] or [1e2 x 1e7] matrix.

Answer 1

[Jan]

index    = (rd(ind, :) >= r | td(ind, :) >= t);
D        = C;
D(index) = 1;
gSum     = sum(prod(D, 2));

[Andrei Bobrov]

+1! Nice!

Small fixed:

D = ones(numel(ind),1)*C(:)';

Answer 2

[Andrei Bobrov]

[ii,jj] = find(rd(ind,:) < r & td(ind,:) < t); 
gSum = sum(accumarray(ii,C(jj),[],@(x)prod(x)));