Because x is a floating-point number, whereas your function expects
only integer arguments, but doesn't enforce that fact.
Alternatively it would also would help if you modified 'set samples'
along with the xrange such that all sampling points are integers. Try
set samples 101
plot [-10:91] sum(x)
In the case at hand: yes, because there's a closed-form solution for
the finite geometrical series. Find it in your Mittelstufe maths
textbook (ca. Klasse 8 oder 9) ;-)
But not generally. gnuplot is not a heavy-duty mathematical analysis
tool. If you want that, get MuPAD, Octave or SciLab instead.
Hans-Bernhard Broeker ( XXXX@XXXXX.COM )
Even if all the snow were burnt, ashes would remain.