scipy.special.betaln

scipy.special.betaln(a, b, out=None) = <ufunc 'betaln'>

Natural logarithm of absolute value of beta function.

Computes ln(abs(beta(a, b))).

Parameters:

a, barray_like

Positive, real-valued parameters

outndarray, optional

Optional output array for function values

Returns:

scalar or ndarray

Value of the betaln function

See also

gamma

the gamma function

betainc

the regularized incomplete beta function

beta

the beta function

Examples

>>> import numpy as np
>>> from scipy.special import betaln, beta

Verify that, for moderate values of a and b, betaln(a, b) is the same as log(beta(a, b)):

>>> betaln(3, 4)
-4.0943445622221

>>> np.log(beta(3, 4))
-4.0943445622221

In the following beta(a, b) underflows to 0, so we can’t compute the logarithm of the actual value.

>>> a = 400
>>> b = 900
>>> beta(a, b)
0.0

We can compute the logarithm of beta(a, b) by using betaln:

>>> betaln(a, b)
-804.3069951764146