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gplus

(Not recommended) Add arrays from workers in an spmd block

    gplus is not recommended. Use spmdPlus instead. For more information, see Version History.

    Description

    example

    C = gplus(A) add the arrays A stored on each worker in the current spmd block or communicating job.

    Tip

    When you offload computations using parfor and parfeval, each computation is run by only one worker at a time. These workers are independent and do not communicate with each other. If you use gplus on these workers, then C is equal to A.

    The function gplus adds the arrays when A has a compatible size on each worker.

    If numlabs is equal to 1, C is equal to A. numlabs is equal to 1 outside of an spmd block or communicating job.

    C = gplus(A,destination) computes the sum of the arrays and stores the result on only one worker. On the worker with labindex equal to destination, C is equal to the sum. On all other workers, C is [].

    Examples

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    This example shows how to use gplus to add a scalar held on each worker in an spmd block.

    Create a parallel pool with 4 workers.

    parpool(4);

    When you execute an spmd block after creating a parallel pool, by default all available workers in the pool will run the code inside the spmd block.

    Run labindex on each worker in the spmd block, and store the result in a scalar A. Use gplus to add the value of A from each worker.

    When you use gplus, by default the result is stored on every worker. On the client, C is a Composite array. To get the result, index into the Composite array.

    spmd
        A = labindex;
        C = gplus(A);
    end
    disp(C{1})
         10

    Input Arguments

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    Input array, specified as a scalar, vector, matrix, or multidimensional array.

    Example: magic(3)

    Index of target worker, specified as a positive integer scalar. The value must be less than or equal to the value given by numlabs, the number of workers running the current spmd block or communicating job. When specified, the result of gplus(A,destination) is only stored on one worker. On the worker with labindex equal to destination, C is equal to the sum. On all other workers, C is [].

    Example: 1

    Algorithms

    When you use gplus(A), the value of A on each worker is added to the value on other workers.

    Diagram showing how four workers combine arrays specified as A into a single array, C.

    Version History

    Introduced in R2006b

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    See Also