MATLAB PARALLEL COMPUTING TOOLBOX - S Uživatelská příručka stáhnout pdf (Strana 56)

100

101

2 Parallel for-Loops (parfor)

2-28

After the first level, you can use any type of valid MATLAB indexing in the second and

further levels.

The variable A shown here on the left is not sliced; that shown on the right is sliced:

A.q{i,12} A{i,12}.q

Fixed Index Listing. Within the first-level parentheses or braces of a sliced variable’s

indexing, the list of indices is the same for all occurrences of a given variable.

The variable A shown here on the left is not sliced because A is indexed by i and i+1 in

different places; the code on the right shown on the right slices A:

Not sliced Sliced

parfor i = 1:k

B(:) = h(A(i), A(i+1));

end

parfor i = 1:k

B(:) = f(A(i));

C(:) = g(A{i});

end

The example above on the right shows some occurrences of a sliced variable with first-

level parenthesis indexing and with first-level brace indexing in the same loop. This is

acceptable.

The following example on the left does not slice A because the indexing of A is not the

same in all places. The example on the right slices A and B. The indexing of A is not the

same as the indexing of B, but all indexing of A is consistent, and all indexing of B is

consistent.

Not sliced Sliced

parfor i=1:10

b = A(1,i) + A(2,i)

end

A = [ 1 2 3 4 5 6 7 8 9 10;

10 20 30 40 50 60 70 80 90 100];

B = zeros(1,10);

parfor i=1:10

for n=1:2

B(i) = B(i)+A(n,i)

end

Form of Indexing. Within the list of indices for a sliced variable, one of these indices is

of the form i, i+k, i-k, k+i, or k-i, where i is the loop variable and k is a constant or

1 2 ... 51 52 53 54 55 56 57 58 59 60 61 ... 655 656

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