Maxima Function
unsum (f, n)
Returns the first backward difference f(n) - f(n - 1)
.
Thus unsum
in a sense is the inverse of sum
.
Examples:
(%i1) g(p) := p*4^n/binomial(2*n,n); n p 4 (%o1) g(p) := ---------------- binomial(2 n, n) (%i2) g(n^4); 4 n n 4 (%o2) ---------------- binomial(2 n, n) (%i3) nusum (%, n, 0, n); 4 3 2 n 2 (n + 1) (63 n + 112 n + 18 n - 22 n + 3) 4 2 (%o3) ------------------------------------------------ - ------ 693 binomial(2 n, n) 3 11 7 (%i4) unsum (%, n); 4 n n 4 (%o4) ---------------- binomial(2 n, n)