return value optimization when overwriting

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Federico
Federico 2012-2-7
Consider the following scenario.
function A=frobnicate(A)
A(1)=1;
end
X=zeros(2000,2000);
X=frobnicate(X);
By inspecting variables with `format debug`, one can see that Matlab (even in R2011b) makes an unnecessary copy of the whole 2000x2000 matrix when it calls the function in the last row. Is there a way to avoid the copy and let the function work on the data "in-place"?
I know about global variables and handle objects, but I read that both are quite inefficient and I doubt that they will actually make something like the above code faster.

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回答（2 个）

Jan
Jan 2012-2-7
No, unfortuantely you cannot force Matlab to work inplace.
See Answers: Missing: Call by reference.
Federico
Federico 2012-2-14
It seems that you can indeed, see http://blogs.mathworks.com/loren/2007/03/22/in-place-operations-on-data/?
I cannot understand how it works exactly, though, the return addresses inspected with "format debug" seem to change, but the time speedup is there.

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