MATLAB PARALLEL COMPUTING TOOLBOX - S Guide de l'utilisateur télécharger pdf (Page 49)

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101

Variables and Transparency in parfor-Loops

2-21

temp = struct();

temp.myfield1 = rand();

temp.myfield2 = i;

end

parfor i = 1:4

temp = struct('myfield1',rand(),'myfield2',i);

end

Slicing Structure Fields

You cannot use structure fields as sliced input or output arrays in a parfor-loop; that is,

you cannot use the loop variable to index the elements of a structure field. For example,

in the following code both lines in the loop generate a classification error because of the

indexing:

parfor i = 1:4

outputData.outArray1(i) = 1/i;

outputData.outArray2(i) = i^2;

end

The workaround for sliced output is to employ separate sliced arrays in the loop, and

assign the structure fields after the loop is complete, as shown in the following code.

parfor i = 1:4

outArray1(i) = 1/i;

outArray2(i) = i^2;

end

outputData = struct('outArray1',outArray1,'outArray2',outArray2);

The workaround for sliced input is to assign the structure field to a separate array before

the loop, and use that new array for the sliced input.

inArray1 = inputData.inArray1;

inArray2 = inputData.inArray2;

parfor i = 1:4

temp1 = inArray1(i);

temp2 = inArray2(i);

end

Scalar Expansion with Sliced Outputs

You cannot use scalar expansion to define a set of values assigned to a sliced output

array. For example, the following code attempts to expand the value idx for assignment

to each element of the vector defined by x(:,idx); this generates an error.

1 2 ... 44 45 46 47 48 49 50 51 52 53 54 ... 655 656

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MATLAB PARALLEL COMPUTING TOOLBOX - S Guide de l'utilisateur Page 49

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