The reference link in my post documents the behavior of sum([]) and prod([]) (although the prod part only says the result is nonzero value).

–Loren

A further advantage of having sum([])==0 and prod([])==1 is that it’s consistent with array concatenation, e.g. prod([A;B]) and (prod(A).*prod(B)) remain equal when A or B are empty.

I often find sum([]) and prod([]) useful, but the help documents are strangely silent on their treatment. Is it unofficial/unsupported functionality because of the controversy, or just something that was forgotten to be mentioned in the help docs?

I will SO take you up on that offer. Can’t wait for a good reason to visit now. Especially if the shucking tools are around as well :-)

–Loren

Thanks for your thoughts.

One way to think about why empty shouldn’t error for sum is the following. Suppose I have a list of some entities. And I want the sum for all the ones greater than a certain value, say 0. That list may be empty, but the sum is then 0. Works for me without having to special case code then.

–Loren

IMHO, sum([]) and prod([]) should throw an error, as most of the times it shows that some kind of error happened before and somehow the variable became unexpectedly empty.

It is very much like asking to calculate the sum of a string.
:)

Initializing with an empty to start a concatenation process makes lots of sense and is good coding style in cases where you can’t predetermine the final size, and therefore preallocate.

–Loren

Implicitly there are trailing 1 dimensions for all arrays in MATLAB. But they do get dropped by ndims, for example, after dimension 2. So it can trip up code like you have seen.

–Loren

Check out the function bsxfun. It will do exactly what you are hoping - not expanding vectors to arrays in order to add different constants to each column, for example.

–Loren

function s=sizex(x);s=size(x);s(end+1:5)=1;

This highlights the occasional case of the 0-by-0-by-1-by-… empty being considered somehow superior to other empties. Consider this sequence:

sizex( num2cell( zeros( 3, 1 ) ) ) = [3 1 1 1 1]
sizex( num2cell( zeros( 2, 1 ) ) ) = [2 1 1 1 1]
sizex( num2cell( zeros( 1, 1 ) ) ) = [1 1 1 1 1]
sizex( num2cell( zeros( 0, 1 ) ) ) = [0 0 1 1 1]  % expected: [0 1 1 1 1]

This num2cell quirk often trips up my code and forces me to insert special-case handling for empties.