MATLAB: Variable H1 can not be classified in parfor-loop

parallel computingparfor

 H1(subsizeX,subsizeY,(subnumX-1)*(subnumY-1))=zeros(subsizeX,subsizeY);
      parfor ii=1:(subnumX-1)*(subnumY-1)
          iiy=ceil(ii/subnumX);
          iix=ii-(iiy-1)*subnumX;
          i1=iix+(iiy-1)*(subnumX-1);
          i2=iix+(iiy-1)*subnumX;
          H1(subsizeX,subsizeY,i1)=HGroup(:,:,i2);
      end

Best Answer

Take a read here for "sliced variables" https://www.mathworks.com/help/distcomp/sliced-variable.html

      parfor ii=1:(subnumX-1)*(subnumY-1)
          iiy = ceil(ii/subnumX);
          iix = ii-(iiy-1)*subnumX;
          i1 = iix+(iiy-1)*(subnumX-1);
          i2 = iix+(iiy-1)*subnumX;
          H1(subsizeX,subsizeY,i1)=HGroup(:,:,i2);  << CAN'T DO THIS. 
          % H1 must be accessed with respect to parfor counter variable, "ii". 
          % Example:
          %   H1{ii} = zeros(ii+1, ii); will work. H{ii} doesn't depend on H{ii+1} , etc.
          % Can't change the sliced variable index via a computation either, because then 
          % each parallel iteration may not always be independent.
          % Bad Example:
          %  H1(ii) = H1(ii+1); %Can't be used. H(ii) depends on H1(ii+1). Not independent for parfor.
          %
      end

Related Solutions

MATLAB: Vectorize a parfor loop to save time

I've looked through the code and it is mostly vectorized already. See comments though for minor improvements. At this point, you'll have to test out different matlab operations to see if you can find a shortcuts, prevent unnecessary matrix copies, etc. You are essentially doing micro-optimization, which is often time-consuming but could be worth it, depending on speed requirements.

As for parfor, see comment above. It seems difficult to vectorize the parallel computing of subsolverCB.

%function [hSub,pSub] = subsolverCB(s1, h1hat, tau, alpha, kappa, gamma, nIn, HGroup, pInit, flag)
function [hSub,pSub] = subsolverCB(s1, h1hat, tau, alpha, kappa, gamma, nIn, hSub, pInit, flag)
[m,n] = size(h1hat);
%hSub = HGroup; %Why do you need 2 copies of HGroup? How about just replacing input HGroup with hSub?
hcheck = hSub;  
c = size(pInit,2)/2;
Es = zeros(size(h1hat));
errSub = zeros(nIn,1);
if flag %== 1 , no need to check flag==1 if flag is either true or false
    px = pInit(1:m-1,1:n-1);
    py = pInit(1:m-1,c+1:c+n-1);
    Es(1:end-1,1:end-1) = s1;
end
% iterationSub = 1;
% while iterationSub <= nIn
tmpC1 = gamma*h1hat - tau*gamma*alpha*Es; %To prevent repeated calculations in for loop
for iterationSub = 1:nIn
    hld = hSub; %hold = hSub; %don't override matlab function "hold", used for holding plots.
    [hx, hy] = grad2(hcheck);
    if flag %== 1  
        Rhx = hx(1:end-1,1:end-1);
        Rhy = hy(1:end-1,1:end-1);
    end
    ptildex = px + kappa*Rhx;
    ptildey = py + kappa*Rhy;
      Denom2 = ptildex.^2+ptildey.^2;  %Denom = sqrt(ptildex.^2+ptildey.^2); %don't sqrt early to save computing power
      MaxDenom = sqrt(max(Denom2, 1)); %sqrt for a smaller set saves time
      px = ptildex ./ MaxDenom; %max(Denom, 1);  
      py = ptildey ./ MaxDenom; %max(Denom, 1);
      if flag %== 1
          %PPtmp = [px,zeros(m-1,1),py,zeros(m-1,1)];
          %PP = [PPtmp;zeros(1,size(PPtmp,2))]; %Why not just initialize in one shot?
          PP = vercat([px,zeros(m-1,1),py,zeros(m-1,1)], zeros(1, size(PPtmp, 2)));
      end
      %Edivp = div2(PP);
      %htilde = hSub + gamma*(Edivp); 
      htilde = hSub + gamma*(div2(PP)); %condensing into 1 line
      %tmp = (tau*htilde + gamma*h1hat - tau*gamma*alpha*Es)/(tau+gamma); %Prevent repeated calculation( "gamma*h1hat, tau*gamma*alpha*Es, etc.
      tmp = (tau*htilde + tmpC1)/(tau+gamma);
      hSub = max(min(tmp,1),0);
      hcheck = 2*hSub - hld;  
      errSub(iterationSub) = norm(hSub-hld,'fro');
  end
  pSub = [px py];

See if you can avoid creating temporary variable px and py, which is just a subset of pInit.

MATLAB: Getting an error “INDEX OUT OF BOUNDS” in the matlab program. Please help.

for i=1:3 
    fepsn(i)=i; % (i) was added to avoid overwriting of the variable 
end

Best Answer

Related Solutions

MATLAB: Vectorize a parfor loop to save time

MATLAB: Getting an error “INDEX OUT OF BOUNDS” in the matlab program. Please help.

Related Question