stable_pdf: Compute values of a (normalized) stable density
In stabreg: Linear Regression with the Stable Distribution

Compute stable pdf values. Admissible range for beta is -1 to 1. If b is not 0, admissible values of alpha are 0.5 < a < 0.9 and 1.1 < a <= 2.

1	stable_pdf(x, a, b)

`x`	values at which to evaluate the density
`a`	alpha value. Either a scalar or vector of length equal to `x` if different values for each observations are assumed
`b`	beta value. Either a scalar or vector of length equal to `x` if different values for each observations are assumed