Going back from cumsum for a matrix

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valentino dardanoni 2022-10-21

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评论： valentino dardanoni 2022-10-21

采纳的回答： David Hill

Suppose I cumsum a matrix, say A=rand(3,3); B=cumsum(A).

Knowing B, how to I get back to A, in a reasonably efficient way, for a rather large B?

Thanks!

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valentino dardanoni 2022-10-21

Thankyou David (and Walter). It works perfectly in my application.

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David Hill 2022-10-21

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https://ww2.mathworks.cn/matlabcentral/answers/1832003-going-back-from-cumsum-for-a-matrix#answer_1080203

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A=round(rand(100,100),4);
B=cumsum(A);
a=round([B(1,:);diff(B)],4);
isequal(A,a)
ans = logical
   1

Key points here are the use of diff(), the duplication of the first entry, and the rounding or other way of comparing with tolerance for the cross-check (since you would need to deal with round-off errors.)

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