How to optimize the following function

Hello everyone:)

It's somewhat a crosspost from stackoverflow http://stackoverflow.com/questions/21146693/sensibility-of-converting-matlab-program-in-java-to-improve-performance. We try to develop a genetic algorithm approach to find a solution to the sudoku game. We've noticed that the code takes too long to calculate one generation and after profiling it found out that the following function takes most of the time, the hotspot (as expected) is the call to

intersect(s,board(i,:))

I think it's because it runs in a loop. Is there a non-loop alternative to compute the difference. Basically we want to find out how many duplicates each row have (in the range of possible values from 1 to 9). Here is the code:

%%%used this code to make a post on stackoverflow
%http://stackoverflow.com/questions/21146693/sensibility-of-converting-matlab-program-in-java-to-improve-performance

    function [fitness, finished,d, threshold]=fitness(population_, n)
    finished=false;
    threshold=false;
    V=ones(n,1);
    d=zeros(size(population_,2),1);
    s=[1:1:n];
    for z=1:size(population_,2)
        board=population_{z};
        t=0;
        l=0;
        for i=1:n
            l=l+n-length(intersect(s,board(:,i)'));
            t=t+n-length(intersect(s,board(i,:)));

        end
        k=sum(abs(board*V-t));

        f=t+l+k/50;
        if t==2 &&l==2
            threshold=true;
        end
        if f==0
            finished=true;        
        else
            fitness(z)=1/f;
            d(z)=f;
        end
    end
    end

Thank you loads

Answer 1

[Walter Roberson]

histc(V, 1:9) > 1

you can then any() that if you just want to know if there are duplicates at all, or you can sum() it if you want to know how many distinct digits have duplicates.

Or you could experiment with the timing of sparse(V, 1, 1) > 1 and of accumarray(V(:), 1) > 1

[Sean de Wolski]

Also ismember is significantly faster than intersect

[den]

Oh, thanks a lot. we used histc, it's so much faster