MATLAB PARALLEL COMPUTING TOOLBOX - S Guia do Utilizador descarregar pdf (Página 468)

100

101

11 Functions — Alphabetical List

11-124

Examples

Create a 2-by-22 codistributed array among four workers, and view the global indices on

each lab:

spmd

C = zeros(2,22,codistributor1d(2,[6 6 5 5]));

if labindex == 1

K = globalIndices(C,2) % returns K = 1:6.

elseif labindex == 2

[E,F] = globalIndices(C,2) % returns E = 7, F = 12.

end

K = globalIndices(C,2,3) % returns K = 13:17.

[E,F] = globalIndices(C,2,4) % returns E = 18, F = 22.

end

Use globalIndices to load data from a file and construct a codistributed array

distributed along its columns, i.e., dimension 2. Notice how globalIndices makes the

code not specific to the number of workers and alleviates you from calculating offsets or

partitions.

spmd

siz = [1000,1000];

codistr = codistributor1d(2,[],siz);

% Use globalIndices to figure out which columns

% each worker should load.

[firstCol,lastCol] = globalIndices(codistr,2);

% Call user-defined function readRectangleFromFile to

% load all the values that should go into

% the local part for this worker.

labLocalPart = readRectangleFromFile(fileName, ...

1,siz(1),firstCol,lastCol);

% With the local part and codistributor,

% construct the corresponding codistributed array.

C = codistributed.build(labLocalPart,codistr);

end

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