[new] implementing comparison methods into pdf class

pylot/core/util/pdf.py

@@ -133,15 +133,13 @@ class ProbabilityDensityFunction(object):
             'both operands must be of type ProbabilityDensityFunction'
 
         raise NotImplementedError('implementation of resulting axis unclear - feature pending!')
-        # x0, incr, npts, pdf_self, pdf_other = self.rearrange(other)
-        #
-        # pdf = np.convolve(pdf_self, pdf_other, 'same') * incr
-        #
-        # # shift axis values for correct plotting
-        # midpoint = npts / 2
-        # x0 = incr * midpoint
-        #
-        # return ProbabilityDensityFunction(x0, incr, npts, pdf)
+        x0, incr, npts, pdf_self, pdf_other = self.rearrange(other)
+        pdf = np.convolve(pdf_self, pdf_other, 'same') * incr
+
+        # shift axis values for correct plotting
+        npts *= 2
+        x0 *= 2
+        return ProbabilityDensityFunction(x0, incr, npts, pdf)
 
     def __sub__(self, other):
         assert isinstance(other, ProbabilityDensityFunction), \
@@ -222,6 +220,25 @@ class ProbabilityDensityFunction(object):
         # return the object
         return ProbabilityDensityFunction(x0, incr, npts, pdf)
 
+    def expectation(self):
+        '''
+        returns the expectation value of the actual pdf object
+
+        ..formula::
+                mu_{\Delta t} = \int\limits_{-\infty}^\infty x \cdot f(x)dx
+
+        :return float: rval
+        '''
+
+        rval = 0
+        for n, x in enumerate(self.axis):
+            rval += x * self.data[n]
+        return rval * self.incr
+
+    def standard_deviation(self):
+        pass
+
+
     def commonlimits(self, incr, other, max_npts=1e5):
         '''
         Takes an increment incr and two left and two right limits and returns