Online Algebra Calculator
Many of users do not use powerful Maxima computer algebra system for systematic work, but for ad hoc algebraic calculations – equations, functions, matrixes, etc. only. To do this job, it is not useful to download the whole application from a web site.
-- Option variable: cauchysum Default value: false
When multiplying together sums with inf as their upper limit, if sumexpand is true and cauchysum is true then the Cauchy product will be used rather than the usual product. In the Cauchy product the index of the inner summation is a function of the index of the outer one rather than varying independently.

Example:
(%i1) sumexpand: false$
(%i2) cauchysum: false$
(%i3) s: sum (f(i), i, 0, inf) * sum (g(j), j, 0, inf);
inf inf
==== ====
\ \
(%o3) ( > f(i)) > g(j)
/ /
==== ====
i = 0 j = 0
(%i4) sumexpand: true$
(%i5) cauchysum: true$
(%i6) s;
inf i1
==== ====
\ \
(%o6) > > g(i1 - i2) f(i2)
/ /
==== ====
i1 = 0 i2 = 0(%o1) true (%i2)