Function builtin_lbeta 

fn builtin_lbeta(
    args: &[RValue],
    _: &[(String, RValue)],
) -> Result<RValue, RError>

Natural logarithm of the beta function.

More numerically stable than log(beta(a, b)) for large a or b.

@param a numeric vector @param b numeric vector @return numeric vector of log-beta values