How to reduce the time complexity?

The following code is taking much time to execute. What I wanted to do is.. Dividing the matrix of size 90x90 into 9x9 grids and calculating the angle counts in each range. Its taking a lot of time for computation. But I need to reduce this at any cost. Could not find the solution.

fsrc = sprintf('FeatureVector%d',ii);

    %FeatureVector=zeros([100,8]);
    cnt1=0; cnt2=0; cnt3=0; cnt4=0; cnt5=0; cnt6=0; cnt7=0; cnt8=0;
    p = 1;
    row = 1;
    rlength = size(Gdir,1);
    clength = size(Gdir,2);

    while p<(rlength)
        q = 1;
        while q<(clength)
            for i=p:p+8
                for j=q:q+8
                    if Gdir(i,j)>=-180 && Gdir(i,j)<=-134                    
                        cnt1 = cnt1+1;                
                    elseif Gdir(i,j)>=-135 && Gdir(i,j)<=-89
                        cnt2 = cnt2 + 1;                                    
                    elseif Gdir(i,j)>=-90 && Gdir(i,j)<=-44
                        cnt3 = cnt3 + 1;                
                    elseif Gdir(i,j)>=-45 && Gdir(i,j)<=-1
                        cnt4 = cnt4 + 1;                
                    elseif Gdir(i,j)>=0 && Gdir(i,j)<=45
                        cnt5 = cnt5 + 1;                
                    elseif Gdir(i,j)>=46 && Gdir(i,j)<=90                   
                        cnt6 = cnt6 + 1;                
                    elseif Gdir(i,j)>=91 && Gdir(i,j)<=135                    
                        cnt7 = cnt7 + 1;                                
                    else                        
                        cnt8 = cnt8 + 1;
                    end                      
                    eval([fsrc '(row,1) = cnt1;']);
                    eval([fsrc '(row,2) = cnt2;']);
                    eval([fsrc '(row,3) = cnt3;']);
                    eval([fsrc '(row,4) = cnt4;']);
                    eval([fsrc '(row,5) = cnt5;']);
                    eval([fsrc '(row,6) = cnt6;']);
                    eval([fsrc '(row,7) = cnt7;']);
                    eval([fsrc '(row,8) = cnt8;']);                                     
                end                               
            end           
            q = q + 9;  row = row+1;        
            cnt1=0; cnt2=0; cnt3=0; cnt4=0; cnt5=0; cnt6=0; cnt7=0; cnt8=0;                    
        end         
        p = p + 9;        
    end        
   dst = sprintf('FV%d.mat',ii);
    s = ['save ./FeatureVectors/' dst ' ' fsrc ';'];
    eval(s);

Answer 1

[Sean de Wolski]

Well first off, don't use eval(); it's evil and slow.

Second, considering that row never changes, you don't need to icncrement row each time. But then again this is what I would do instead of using eval and cnt1:cnt5

     if Gdir(i,j)>=-180 && Gdir(i,j)<=-134                    
                        fsrc(row,1) = fsrc(row,1)+1;                
                    elseif Gdir(i,j)>=-135 && Gdir(i,j)<=-89

etc.

Also, it looks like you're just doing a histogram:

fsrc = histc(Gdir(:),[-180 -134 -89 etc.])

And, most importantly, use the profiler to profile your code and identify bottlenecks.

[.. Vamshi]

Oh..Ya Thanks alot. I'll try the suggested changes.