[Pymc-user] poisson for negative values

[Seth de l'I. <sz...@ub...>]

Hello,

I was expecting a poisson prior to limit a parameter to possitive values
much like using the exponential prior would.  Instead it halted
processing.

    >>> from PyMC.MCMC import *
    >>> class foo(MetropolisHastings): pass
    ...
    >>> f = foo()
    >>> f.exponential_prior(-1, 5)
    nan
    >>> f.poisson_prior(-1, 5)
    PAUSE  negative factorial in factln statement executed
    To resume execution, type go.  Other input will terminate the job.

    STOP

Shouldn't poisson_prior and poisson_like return nan as well?

Thanks,
  Seth

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