How to create and empty matrix of a given size in a way that is compatible with codegen

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John Edwards 2022-5-11

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https://ww2.mathworks.cn/matlabcentral/answers/1716590-how-to-create-and-empty-matrix-of-a-given-size-in-a-way-that-is-compatible-with-codegen

评论： John Edwards 2022-5-11

采纳的回答： Richard McCormack

I have a function that is writing to an output matrix (y).

I can create y in the function using:

y = zeros(size(x));

x is a variable size large array and using zeros() is inefficient because it initializes the array with zeros that are then going to be overwritten.

I was wondering if there is a way to do this more efficiently?

I've tried a lot of the options I can find so far but none are compatible with codegen.

Thanks very much, as always,

John

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KSSV 2022-5-11

You want to initialize and then do what?

John Edwards 2022-5-11

Codegen requires that the size of the array is declared before use so I'd like to declare it and then fill it with the appropriate output values, rather than using the zeros function, which is then overwritten by the output data.

Best,

John

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Answer 1

Richard McCormack 2022-5-11

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编辑：Richard McCormack 2022-5-11

Hi John,

I think coder.nullcopy is what you are looking for:

https://www.mathworks.com/help/coder/ref/coder.nullcopy.html

Be aware that this function is 'unsafe', in the sense that you can access uninitialized memory after using it.

Best,

Richard

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John Edwards 2022-5-11

Fantastic answer, Richard,

Worked like a dream :-)

J

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