Addining py files

dice.py

@@ -0,0 +1,39 @@
+"""This file contains code for use with "Think Bayes",
+by Allen B. Downey, available from greenteapress.com
+
+Copyright 2012 Allen B. Downey
+License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
+"""
+
+from thinkbayes import Suite
+
+
+class Dice(Suite):
+    """Represents hypotheses about which die was rolled."""
+
+    def Likelihood(self, data, hypo):
+        """Computes the likelihood of the data under the hypothesis.
+
+        hypo: integer number of sides on the die
+        data: integer die roll
+        """
+        # write this method
+        return 1
+
+
+def main():
+    suite = Dice([4, 6, 8, 12, 20])
+
+    suite.Update(6)
+    print 'After one 6'
+    suite.Print()
+
+    for roll in [8, 7, 7, 5, 4]:
+        suite.Update(roll)
+
+    print 'After more rolls'
+    suite.Print()
+
+
+if __name__ == '__main__':
+    main()

dice_soln.py

@@ -0,0 +1,41 @@
+"""This file contains code for use with "Think Bayes",
+by Allen B. Downey, available from greenteapress.com
+
+Copyright 2012 Allen B. Downey
+License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
+"""
+
+from thinkbayes import Suite
+
+
+class Dice(Suite):
+    """Represents hypotheses about which die was rolled."""
+
+    def Likelihood(self, data, hypo):
+        """Computes the likelihood of the data under the hypothesis.
+
+        hypo: integer number of sides on the die
+        data: integer die roll
+        """
+        if hypo < data:
+            return 0
+        else:
+            return 1.0/hypo
+
+
+def main():
+    suite = Dice([4, 6, 8, 12, 20])
+
+    suite.Update(6)
+    print 'After one 6'
+    suite.Print()
+
+    for roll in [8, 7, 7, 5, 4]:
+        suite.Update(roll)
+
+    print 'After more rolls'
+    suite.Print()
+
+
+if __name__ == '__main__':
+    main()

euro.py

@@ -0,0 +1,52 @@
+"""This file contains code used in "Think Stats",
+by Allen B. Downey, available from greenteapress.com
+
+Copyright 2013 Allen B. Downey
+License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
+"""
+
+"""This file contains a partial solution to a problem from
+MacKay, "Information Theory, Inference, and Learning Algorithms."
+
+    Exercise 3.15 (page 50): A statistical statement appeared in
+    "The Guardian" on Friday January 4, 2002:
+
+        When spun on edge 250 times, a Belgian one-euro coin came
+        up heads 140 times and tails 110.  'It looks very suspicious
+        to me,' said Barry Blight, a statistics lecturer at the London
+        School of Economics.  'If the coin weere unbiased, the chance of
+        getting a result as extreme as that would be less than 7%.'
+
+MacKay asks, "But do these data give evidence that the coin is biased
+rather than fair?"
+
+"""
+
+import thinkbayes
+import thinkplot
+
+
+class Euro(thinkbayes.Suite):
+
+    def Likelihood(self, data, hypo):
+        """Computes the likelihood of the data under the hypothesis.
+
+        hypo: integer value of x, the probability of heads (0-100)
+        data: string 'H' or 'T'
+        """
+        # fill this in!
+        return 1
+
+
+def main():
+    suite = Euro(range(0, 101))
+
+    suite.Update('H')
+
+    thinkplot.Pmf(suite)
+    thinkplot.Show(xlabel='x',
+                ylabel='Probability')
+
+
+if __name__ == '__main__':
+    main()

euro2.py

@@ -0,0 +1,85 @@
+"""This file contains code used in "Think Stats",
+by Allen B. Downey, available from greenteapress.com
+
+Copyright 2013 Allen B. Downey
+License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
+"""
+
+"""This file contains a partial solution to a problem from
+MacKay, "Information Theory, Inference, and Learning Algorithms."
+
+    Exercise 3.15 (page 50): A statistical statement appeared in
+    "The Guardian" on Friday January 4, 2002:
+
+        When spun on edge 250 times, a Belgian one-euro coin came
+        up heads 140 times and tails 110.  'It looks very suspicious
+        to me,' said Barry Blight, a statistics lecturer at the London
+        School of Economics.  'If the coin weere unbiased, the chance of
+        getting a result as extreme as that would be less than 7%.'
+
+MacKay asks, "But do these data give evidence that the coin is biased
+rather than fair?"
+
+"""
+
+import thinkbayes
+
+
+class Euro(thinkbayes.Suite):
+
+    def Likelihood(self, hypo, data):
+        """Computes the likelihood of the data under the hypothesis.
+
+        hypo: integer value of x, the probability of heads (0-100)
+        data: tuple (#heads, #tails)
+        """
+        x = hypo / 100.0
+        heads, tails = data
+        like = x**heads * (1-x)**tails
+        return like
+
+
+def AverageLikelihood(suite, data):
+    """Computes the average likelihood over all hypothesis in suite.
+
+    Args:
+      suite: Suite of hypotheses
+      data: some representation of the observed data
+
+    Returns:
+      float
+    """
+    total = 0
+
+    for hypo, prob in suite.Items():
+        like = suite.Likelihood(hypo, data)
+        total += prob * like
+
+    return total
+
+
+def main():
+    fair = Euro()
+    fair.Set(50, 1)
+
+    bias = Euro()
+    for x in range(0, 101):
+        if x != 50:
+            bias.Set(x, 1)
+    bias.Normalize()
+
+    # notice that we've changed the representation of the data
+    data = 140, 110
+
+    like_bias = AverageLikelihood(bias, data)
+    print 'like_bias', like_bias
+
+    like_fair = AverageLikelihood(fair, data)
+    print 'like_fair', like_fair
+
+    ratio = like_bias / like_fair
+    print 'Bayes factor', ratio
+
+
+if __name__ == '__main__':
+    main()

euro2_soln.py

@@ -0,0 +1,90 @@
+"""This file contains code used in "Think Stats",
+by Allen B. Downey, available from greenteapress.com
+
+Copyright 2013 Allen B. Downey
+License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
+"""
+
+"""This file contains a partial solution to a problem from
+MacKay, "Information Theory, Inference, and Learning Algorithms."
+
+    Exercise 3.15 (page 50): A statistical statement appeared in
+    "The Guardian" on Friday January 4, 2002:
+
+        When spun on edge 250 times, a Belgian one-euro coin came
+        up heads 140 times and tails 110.  'It looks very suspicious
+        to me,' said Barry Blight, a statistics lecturer at the London
+        School of Economics.  'If the coin weere unbiased, the chance of
+        getting a result as extreme as that would be less than 7%.'
+
+MacKay asks, "But do these data give evidence that the coin is biased
+rather than fair?"
+
+"""
+
+import thinkbayes
+import thinkplot
+
+
+class Euro(thinkbayes.Suite):
+
+    def Likelihood(self, hypo, data):
+        """Computes the likelihood of the data under the hypothesis.
+
+        hypo: integer value of x, the probability of heads (0-100)
+        data: tuple (#heads, #tails)
+        """
+        x = hypo / 100.0
+        heads, tails = data
+        like = x**heads * (1-x)**tails
+        return like
+
+
+def AverageLikelihood(suite, data):
+    """Computes the average likelihood over all hypothesis in suite.
+
+    Args:
+      suite: Suite of hypotheses
+      data: some representation of the observed data
+
+    Returns:
+      float
+    """
+    total = 0
+
+    for hypo, prob in suite.Items():
+        like = suite.Likelihood(hypo, data)
+        total += prob * like
+
+    return total
+
+
+def main():
+    fair = Euro()
+    fair.Set(50, 1)
+
+    bias = Euro()
+    for x in range(0, 51):
+        bias.Set(x, x)
+    for x in range(51, 101):
+        bias.Set(x, 100-x)
+    bias.Normalize()
+
+    thinkplot.Pmf(bias)
+    thinkplot.Show()
+
+    # notice that we've changed the representation of the data
+    data = 140, 110
+
+    like_bias = AverageLikelihood(bias, data)
+    print 'like_bias', like_bias
+
+    like_fair = AverageLikelihood(fair, data)
+    print 'like_fair', like_fair
+
+    ratio = like_bias / like_fair
+    print 'Bayes factor', ratio
+
+
+if __name__ == '__main__':
+    main()

euro_soln.py

@@ -0,0 +1,55 @@
+"""This file contains code used in "Think Stats",
+by Allen B. Downey, available from greenteapress.com
+
+Copyright 2013 Allen B. Downey
+License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
+"""
+
+"""This file contains a partial solution to a problem from
+MacKay, "Information Theory, Inference, and Learning Algorithms."
+
+    Exercise 3.15 (page 50): A statistical statement appeared in
+    "The Guardian" on Friday January 4, 2002:
+
+        When spun on edge 250 times, a Belgian one-euro coin came
+        up heads 140 times and tails 110.  'It looks very suspicious
+        to me,' said Barry Blight, a statistics lecturer at the London
+        School of Economics.  'If the coin weere unbiased, the chance of
+        getting a result as extreme as that would be less than 7%.'
+
+MacKay asks, "But do these data give evidence that the coin is biased
+rather than fair?"
+
+"""
+
+import thinkbayes
+import thinkplot
+
+
+class Euro(thinkbayes.Suite):
+
+    def Likelihood(self, data, hypo):
+        """Computes the likelihood of the data under the hypothesis.
+
+        hypo: integer value of x, the probability of heads (0-100)
+        data: string 'H' or 'T'
+        """
+        x = hypo / 100.0
+        if data == 'H':
+            return x
+        else:
+            return 1-x
+
+
+def main():
+    suite = Euro(range(0, 101))
+
+    suite.Update('H')
+
+    thinkplot.Pmf(suite)
+    thinkplot.Show(xlabel='x',
+                ylabel='Probability')
+
+
+if __name__ == '__main__':
+    main()