Incomplete beta function

`I = betainc(X,Z,W)`

I = betainc(X,Z,W,tail)

`I = betainc(X,Z,W)`

computes
the incomplete beta function for corresponding elements of the arrays `X`

, `Z`

,
and `W`

. The elements of `X`

must
be in the closed interval [0,1]. The arrays `Z`

and `W`

must
be nonnegative and real. All arrays must be the same size, or any
of them can be scalar.

`I = betainc(X,Z,W,tail)`

specifies
the tail of the incomplete beta function. Choices are:

| Computes the integral from |

| Computes the integral from |

These functions are related as follows:

1-betainc(X,Z,W) = betainc(X,Z,W,'upper')

`0`

,
it is more accurate to use the` 'upper'`

option than
to subtract the `'lower'`

value from `1`

.