# How to use Sum and Dot function in GPU computation with arrayfun?

조회 수: 4(최근 30일)
Viraj Gandhi 2022년 12월 28일
댓글: Joss Knight 2022년 12월 29일
I am trying to find a dot product of two arrays. The given code below is an example. I am new to GPU computing and any help is appreciated.
The main function is:
a = [1,2,3,4];
b = [5,6,7,8];
a=gpuArray(a);
b=gpuArray(b);
funOut = arrayfun(@protoDotProd,a,b);
The function where the dot product is below:
function funOut = protoDotProd(a,b)
cTemp = a+b; % Just an example. In reality, lots of operations
%% option1
% funOut = dot(a,cTemp);
%% option2
% funOutTemp = a.*cTemp;
% funOut = sum(funOutTemp);
%% option3
funOut = sum(a .* cTemp);
None of these options are working and giving me an error:
Error using dotTest
Function passed as first input argument contains unsupported or unknown function 'sum' (or 'dot' for option 1).
Error in 'protoDotProd' (line: 6)
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Voss 2022년 12월 28일

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### 채택된 답변

Joss Knight 2022년 12월 28일
You cannot perform vector operations in GPU arrayfun. The a and b arguments to your function are not the whole array, they are the scalar values of each element.
Do your element-wise operations ("lots of operations" in your words, followed by the element-wise multiplication) inside your arrayfun function and then do the sum.
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Joss Knight 2022년 12월 29일
Exactly correct, yes. Except that you can only perform scalar operations on those scalars (so you can't form an array by concatenating the two values for instance).

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