MATLAB: Problem with ‘sum’ command

fftmathematicsmatrixmatrix manipulationsum

hello if i have this code: x=[10,1000] a=sum(x) i get after the sum that a=[1,1000] so i need to find the inverse command for 'sum' to create the original [10,1000] matrix how does i do that? maybe with 'fft'? thanks!

Best Answer

You mean that the size of x is 10x10000, right? Not that x is the vector [10,10000], which is what you wrote.

There is no unique inverse to the sum() command. Think about it. If I tell you that 2+2 equals 4, there is no way to for you to undo that, and obtain 2 and 2 from 4. It could have been 1 and 3, or 0 and 4, or -1.1 and 5.1, etc.

Related Solutions

MATLAB: Meaning of ” if sum(j == I)”

sum(j == I) is counting the number of entries in I that are equal to 1, 2, 3, ... 15322. The "if" around it is an implicit test for non-zero, so it is testing to see if there are any entries at all that match. A better way would be

if any(j == I)

I would suggest, though, that you would probably be better off using

[tf, idx] = ismember(x, I);
for j = idx ...

and probably you would be better off yet inverting the search, like ismember(I, x)

MATLAB: How can i use ‘sum’ for a ‘cell array’

A = cell(4,2) ; 
for i = 1:4
    for j = 1:2
        A{i,j} = rand(1,2) ;
    end
end
B = cellfun(@sum,A)

Best Answer

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MATLAB: Meaning of ” if sum(j == I)”

MATLAB: How can i use ‘sum’ for a ‘cell array’

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