parfeval evaluation is slow
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Hi
I am using parfeval to calculate the eigenvalues of a matrix M with typical dimension of 1500x1500x100. The parfeval evaluations is slow since I read the output just after the evaluation of each matrix M(:,:,k) k=1,..,100. I want to store all the eigenvalues and eigenvectores in the variabel f and read the output after finishing the parfeval evaluation.
Current code:
eigMtr=complex(zeros(2*L,2*NumOfSlabs*L));
W=eigMtr;
W_1=complex(zeros(L,2*NumOfSlabs*L));W_2=W_1;
for k=1:NumOfSlabs
f=parfeval(@eig,3,M(:,:,k));
[Wt,Dt] = fetchOutputs(f);
start=1+(k-1)*2*L;stop=2*k*L;
eigMtr(1:2*L,start:stop)=sqrt(Dt);
W1=Wt(1:L,:);
W2=Wt(L+1:2*L,:);
W_1(:,start:stop)=W1;
W_2(:,start:stop)=W2;
W(1:L,start:stop)=W2;
W(L+1:2*L,start:stop)=W1;
end
I want to do something like this
for k=1:NumOfSlabs
f=parfeval(@eig,3,M(:,:,k));
end
for k=1:NumOfSlabs
[idx,Wt,Dt] = fetchNext(f)
start=1+(k-1)*2*L;stop=2*k*L;
eigMtr(1:2*L,start:stop)=sqrt(Dt);
W1=Wt(1:L,:);
W2=Wt(L+1:2*L,:);
W_1(:,start:stop)=W1;
W_2(:,start:stop)=W2;
W(1:L,start:stop)=W2;
W(L+1:2*L,start:stop)=W1;
end
Thanks for your help
Poul-Erik
采纳的回答
Walter Roberson
2025-4-11
Note the correction to the number of output arguements parameter in the parfeval() call
f = cell(NumOfSlabs, 1);
for k=1:NumOfSlabs
f{k} = parfeval(@eig,2,M(:,:,k));
end
wait(f{1});
for k=1:NumOfSlabs
[Wt,Dt] = fetchOutputs(f{k});
start=1+(k-1)*2*L; stop=2*k*L;
eigMtr(1:2*L,start:stop)=sqrt(Dt);
W1=Wt(1:L,:);
W2=Wt(L+1:2*L,:);
W_1(:,start:stop)=W1;
W_2(:,start:stop)=W2;
W(1:L,start:stop)=W2;
W(L+1:2*L,start:stop)=W1;
end
8 个评论
Poul-Erik Hansen
2025-4-12
Walter Roberson
2025-4-12
Each parfeval() generates a singular future. We write those futures in cell arrays, so when we reference the cell array at a particular location, it is the location of a single future.
I did things this way to duck the question of whether futures could be stored using standard array indexing, which was something I could not find readily documented. However, looking at https://www.mathworks.com/help/matlab/ref/parallel.future.aftereach.html#mw_2abc4dc5-73a6-4a2b-8d9f-c6f09b39f6d5 I see that you can use regular indexing to create an array of futures. So perhaps the flow could be
for k=1:NumOfSlabs
f(k) = parfeval(@eig,3,M(:,:,k));
end
for k=1:NumOfSlabs
[idx,Wt,Dt] = fetchNext(f);
start = 1+(idx-1)*2*L; stop=2*idx*L;
eigMtr(1:2*L,start:stop)=sqrt(Dt);
W1=Wt(1:L,:);
W2=Wt(L+1:2*L,:);
W_1(:,start:stop)=W1;
W_2(:,start:stop)=W2;
W(1:L,start:stop)=W2;
W(L+1:2*L,start:stop)=W1;
end
Poul-Erik Hansen
2025-4-13
Edric Ellis
2025-4-15
@Walter Roberson It is definitely expected that you can create arrays of parallel.Future - both fetchNext and fetchOutputs accept arrays of futures (in particular, fetchNext is only really useful with an array of futures).
Walter Roberson
2025-4-15
The documentation for parfeval() does not show any arrays of futures, so I was under the impression that arrays of futures were potentially only generatable by parfevalOnAll
Edric Ellis
2025-4-15
@Walter Roberson thanks for that - I'll see if we can get an example showing the expected usage on the parfeval page itself. Your comment above has exactly the code I would expect to see.
(A single call to parfevalOnAll returns a scalar parallel.FevalOnAllFuture - and while you can make arrays of these, it isn't as useful, and you can't use those with fetchNext)
Edric Ellis
2025-4-15
Ah, actually, the Parallel Computing Toolbox page for parfeval already does have examples showing arrays https://uk.mathworks.com/help/parallel-computing/parallel.pool.parfeval.html . @Walter Roberson were you looking at the page in the MATLAB doc? https://uk.mathworks.com/help/matlab/ref/parfeval.html .
Walter Roberson
2025-4-15
更多回答（1 个）
Steven Lord
2025-4-11
0 个投票
Have you compared the time of your parfeval call to the time required for a call to the pageeig function?
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