How to slice these variables?

Hi,

can somebody help me to slice these variables in a parfor loop?

indices(:,1) = max(min(ceil(vector(:,1)-Xcoor),nx),1);

indices(:,2) = max(min(ceil(vector(:,2)-Ycoor),ny),1);

indices(:,3) = max(min(ceil(vector(:,3)-Ycoor(idx_parfor)),nz),1);

I currently use the construction:

indices_1 = max(min(ceil(vector(:,1)-Xcoor),nx),1);

indices_2 = max(min(ceil(vector(:,2)-Ycoor),ny),1);

indices_3 = max(min(ceil(vector(:,3)-Ycoor(idx_parfor)),nz),1);

Is there any way to use a single variable indices again? In order to allow for indexing of the variable indices? The parfor variable is of course idx_parfor. An indexed solution would be unavoidable if there are more than 3 indices.

Best Joerg

[Rik]

If it is merely the detection that is preventing execution, you could consider putting this in a separate function.

Also, shouldn't you be using Zcoor in your third call?

[Joerg Pfannmoeller]

Thank you. There is a type-o in indices_3, as you found.

Answer 1

[Edric Ellis]

I think what you're trying to do is something like this, which doesn't work:

N = 4;
out = zeros(N, 3);
try
    parfor idx = 1:N
        out(idx,1) = idx;
        out(idx,2) = -idx;
        out(idx,3) = 2*idx;
    end
catch E
    disp(E.message)
end

Error: Unable to classify the variable 'out' in the body of the parfor-loop. For more information, see Parallel for Loops in MATLAB, "Solve Variable Classification Issues in parfor-Loops".

The way to fix this is to assign a whole column of out all in one indexing expression:

N = 4;
out = zeros(N, 3);
parfor idx = 1:N
    o1 = idx;
    o2 = -idx;
    o3 = 2*idx;
    % Single sliced indexing assignment into `out`
    out(idx,:) = [o1, o2, o3];
end
disp(out)

     1    -1     2
     2    -2     4
     3    -3     6
     4    -4     8

In some situations, you can use for loops inside parfor.

N = 4;
M = 3;
out = zeros(N, M);
parfor idx = 1:N
    % inner for-loop over the columns of `out`
    for jdx = 1:M
        out(idx,jdx) = 1000 * idx + jdx;
    end
end
disp(out)

        1001        1002        1003
        2001        2002        2003
        3001        3002        3003
        4001        4002        4003

[Joerg Pfannmoeller]

Thanks. It works now.