The Maxima on-line user's manual

Algebra Calculator

Unsum

Function: unsum (<f>, <n>) Returns the first backward difference `<f>(<n>) - <f>(<n> - 1)`. Thus `unsum` in a sense is the inverse of `sum`.

See also `nusum`.

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)```

```(%o1)                                true
(%i2) ```

Related Examples

unsum(1/2^x,x);

Calculate

? unsum;

Calculate

f(n) := n^2;

f(8);

unsum (f, n);

Calculate

unsum

unsum(90/(x*x-5*x+4),x);

Calculate

f(n) := n^2;

f(8);

unsum (f, 10);

Calculate

unsum(1/2^x,x);

Calculate

? unsum;

Calculate

f(n) := n^2;

f(8);

unsum (f, n);

Calculate

unsum

unsum(90/(x*x-5*x+4),x);

Calculate

f(n) := n^2;

f(8);

unsum (f, 10);

Calculate