Non distributed arrays in SPMD

I have a distributed array D and a nondistributed C and m workers. I am trying to modify C based on D for all the workers. Here is the code:

X=fopen() %load data from file

C=fopen() %composite array coppied to all workers

[ml,nb,ne]=prange(1,L,matlabpool('size'));

matlabpool 2

spmd D=codistributed(X,codistributor1d(1));

   for i=nb(labindex):ne(labindex) %for-loop on local part of D

      if D(i,1)>10

         C(i)=0 

      end

   end

end

Each worker has a copy of C. The code updates C locally on each worker. I would like to ask if there is any way to update C on all the workers whenever the worker "labindex" set to zero the C(i). One possible way is to gather C on the client but probably will be not so efficient. Thank you in advance for your kind help.

Answer 1

[Jill Reese]

I may be misunderstanding what is returned by your prange function, but if you just want the labs to iterate over the entire local part that they own then it's probably easier to use the distributed array interface to work with your data.

% setup X and C

matlabpool 2

spmd
   D = codistributed(X, codistributor1d(1));
end

% now use D as a distributed array
for i = 1:size(D,1)
   if D(i,1) > 10
      C(i) = 0;
   end
end

Also, if you don't care how D is distributed over the workers, you can replace the spmd block entirely with

D = distributed(X);

D is then distributed over the workers in whatever way that the Parallel Computing Toolbox chooses.

[Georgios]

Dear Jill thank you for your respond. The prange() functions returns the size of each local part of array D (i.e. size(D)=162,5 then for two workers we have D_Local_1=D(1:81) and D_Local_2=D(82:162). My main problem is array C. Even if I define it prior to SPMD it is coppied to each worker (i.e. 2 copies for two workers-composite array). I am trying to modify both coppies of C whenever any of the workers make a change in C. i.e. if D(10,1)=11 then C_copy_of_worker_1(i)=0 and C_copy_of_worker_2(i)=0. So far each worker updates only its local copy of array C.

Thank you again for your help.

[Jill Reese]

Georgios,

I'm sorry; my previous answer is clearly not helpful to you. What are the sizes of X and C initially? Knowing the size of the problem will help me provide a better suggestion.

Best,

Jill