Why numel() is not accepted with a gpuArray

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Song Decn 2022-9-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1805260-why-numel-is-not-accepted-with-a-gpuarray

评论： Song Decn 2022-9-18

采纳的回答： Walter Roberson

pcGpu = gpuArray(5:100);

r = arrayfun( @numel, pcGpu );

simple line of code above, although numel is supported with gpuArray, I still get following feedback:

Function passed as first input argument contains unsupported or unknown function 'numel'.

For more information see Tips.

Am I doing sth. wrong?

Thanks, Song

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Walter Roberson 2022-9-15

Are you applying numel to the entire array, or are you applying numel to each element of an array? When you use arrayfun then by definition the function is passed one element of the array.

arrayfun over a gpuArray does not support anonymous functions with captured variables.

Walter Roberson 2022-9-15

在 MATLAB Online 中打开

for i = 1:numel(a)
    f = pcGpu + i;
end

That overwrites all of f each iteration, so if you could get it to work, the result would be the same as if you had done

i = numel(a);
f = pcGpu + numel(a);

Reminder: you can pass numel(a) in as a parameter.

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采纳的回答

Walter Roberson 2022-9-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1805260-why-numel-is-not-accepted-with-a-gpuarray#answer_1054295

编辑：Walter Roberson 2022-9-15

https://www.mathworks.com/help/parallel-computing/gpuarray.arrayfun.html

numel is not supported inside any function run on a gpuArray by using arrayfun. The above link lists all supported functions.

Remember that arrayfun on a gpuArray runs all aspects on the gpu. Variables not specifically configured as gpuArray have to be converted to gpuArray internally because the entire function runs on the gpu.