Subject: Re: Sum of no numbers
Date: Sat, 16 May 1998 19:20:24 -0400
From: Alex Bogomolny
The questions you ask.
I am pretty sure that in different circumstances both possibilities may prove useful. However, consider this:
sum(A union B) = sum(A) + sum(B)
may be expected to be correct for A and B with empty intersection. In particular, this would imply sum(empty) = 0.
But then again, if you want to get a warning of an attempt to sum over an empty set then the function sum() may as well return NaN. Up to you.