"""This file contains code for use with "Think Bayes",
by Allen B. Downey, available from greenteapress.com
Copyright 2014 Allen B. Downey
License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
"""
from __future__ import print_function, division
import numpy
import thinkbayes2
import thinkplot
class Hyrax(thinkbayes2.Suite):
"""Represents hypotheses about how many hyraxes there are."""
def Likelihood(self, data, hypo):
"""Computes the likelihood of the data under the hypothesis.
hypo: total population
data: # tagged, # caught (n), # of caught who were tagged (k)
"""
tagged, n, k = data
if hypo < tagged + n - k:
return 0
p = tagged / hypo
like = thinkbayes2.EvalBinomialPmf(k, n, p)
return like
class Hyrax2(thinkbayes2.Suite):
"""Represents hypotheses about how many hyraxes there are."""
def Likelihood(self, data, hypo):
"""Computes the likelihood of the data under the hypothesis.
hypo: total population (N)
data: # tagged (K), # caught (n), # of caught who were tagged (k)
"""
N = hypo
K, n, k = data
if hypo < K + (n - k):
return 0
like = thinkbayes2.EvalHypergeomPmf(k, N, K, n)
return like
def main():
hypos = range(1, 1000)
suite = Hyrax(hypos)
suite2 = Hyrax2(hypos)
data = 10, 10, 2
suite.Update(data)
suite2.Update(data)
thinkplot.Pdf(suite, label='binomial')
thinkplot.Pdf(suite, label='hypergeom')
thinkplot.Show()
if __name__ == '__main__':
main()
