incomplete gamma function in python?
Question: the `scipy.special.gammainc` can not take negative values for the first
argument. Are there any other implementations that could in python? I can do a
manual integration for sure but I'd like to know if there are good
alternatives that already exist.

    
    
    Correct result: 1 - Gamma[-1,1] = 0.85
    
    Use Scipy: scipy.special.gammainc(-1, 1) = 0
    

Thanks.


Answer: I typically reach for [mpmath](http://code.google.com/p/mpmath/) whenever I
need special functions and I'm not too concerned about performance. (Although
its performance in many cases is pretty good anyway.)

For example:

    
    
    >>> import mpmath
    >>> mpmath.gammainc(-1,1)
    mpf('0.14849550677592205')
    >>> 1-mpmath.gammainc(-1,1)
    mpf('0.85150449322407795')
    >>> mpmath.mp.dps = 50 # arbitrary precision!
    >>> 1-mpmath.gammainc(-1,1)
    mpf('0.85150449322407795208164000529866078158523616237514084')
    

