Converting for loop to parfor loop

Nick

2013 11 26

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4 次查看（30 天）

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Hi..i am new to matlab and i am having trouble to convert the two 'for' loop below into parfor loop so it takes shorter time to execute.

I tried by just replacing the 'for' to 'parfor' in for the first 'for' loop which i know is not correct and i get a longer execution time? Can anyone explain to me too?

For the second 'for loop' i had an

Error using ==> parallel_function at 598 Error in ==> parallel_function>make_general_channel/channel_general at 894 Undefined function or variable 'irange'.

 for i=2:1:nc
    sum1 = 0.0;
    sum2 = 0.0;
        for j=1:1:nc+1
            if i==j % skipped
            continue;
            end
           dxx = x(1,j) - x(1,i);
           rr=abs(dxx);
            if rr < re
            sum1 = sum1 +  kernel(rr,re,ktype)*rr^nor;
            sum2 = sum2 +  kernel(rr,re,ktype)*rr^(nor-2.0);
            end
       end
    dtt = 0.5* cd * sum1/sum2;
    if dtt < dt
        dt = dtt;
    end
 end

matlabpool open local 2

tic;

% time marching nt=1; time(1,1) = 0.0; error(1,1) = 1.0e-10;

for t=dt:dt:0.1
  nt=nt+1;
  time(1,nt) = t;
    disp(t);
    i_range=2:1:nc;
    j_range=1:1:nc+1;
    parfor loop=1:(numel(i_range)*numel(j_range))
        i=i_range(floor(loop/length(irange))+1);
        j=j_range((floor(mod(loop,length(irange))))+1);
    end
    % get the laplacian for all internal grids
    for i=2:1:nc
        sum = 0.0;
        zeta(1,i) = 0.0;
        for j=1:1:nc+1
            if i==j % skipped
                continue;
            end
            dxx = x(1,j) - x(1,i);
            rr=abs(dxx);
            if rr < re
                sum = sum + (p(nt-1,j)-p(nt-1,i))*kernel(rr,re,ktype)*rr^(nor-2.0);
                zeta(1,i) = zeta(1,i) + kernel(rr,re,ktype)*rr^nor; 
                %sumw(1,i) = sumw(1,i) + kernel(rr,re,1);        
            end
        end
        lapp(1,i) = 2.0*dim*sum/zeta(1,i);
        p(nt,i) = p(nt-1,i) + dt*lapp(1,i);
    end 
    % update boundary value
    p(nt,1) = function_phi(0,t);
    p(nt,nc+1) = function_phi(1,t);
    % calculate L2norm error
    sumerr = 0.0;
    for i=1:1:nc+1
        ptheo = function_phi(x(1,i),t);
        err = (ptheo - p(nt,i));
        sumerr = sumerr + err*err;
    end
    sumerr = sqrt(sumerr);
    disp(sumerr);
    error(1,nt) = sumerr;