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`ibeta(`

`x`, `a`, `b` [, /complement])

Returns the incomplete beta function: integral over `t`

from 0 to

of `x``t^(`

, for `a`-1) (1 - t)^(`b`-1) /
beta(`a`,`b`)

between 0 and 1 (inclusive)
and `x`

, `a`

positive. If keyword
`b``/complement`

is specified, then one minus this value is returned.
Minus one is returned for illegal parameter combinations.

See also: beta