Inappropriate MATLAB warning when summing over columns

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Kaushik Lakshminarasimhan
评论： Kaushik Lakshminarasimhan 2017-11-5
Suppose X is an Nx10 matrix and I want to sum over each of the 10 columns, regardless of number of rows. I use:
Y = sum(X);
However, N can sometimes be equal to 1 in which case X only has one row. The above operation will now sum over the elements of that row. To avoid this, I change my operation to:
Y = sum(X',2)
which works for any generic N. Now when I hover my cursor over "sum", I see the following warning: Instead of using transpose ('), consider using a different DIMENSION input argument to SUM. I find this warning misleading because clearly the alternative won't work. Is there an alternative to using transpose in my case?

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Guillaume
Guillaume 2017-11-5
The warning is entirely accurate, if you want sum(X) to sum across the rows whether or not X is a vector (i.e. sum will always return a vector of size 1 x size(X, 2), then you should use
Y = sum(X, 1);
Your Y = sum(X', 2) is also the same as Y = sum(X, 1)' and is never equivalent to your Y=sum(X) (it's the conjugate transpose for non-vectors).

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