symbolic_probability.py 文件源码

def doit(self, **hints):
        arg1 = self.args[0]
        arg2 = self.args[1]
        condition = self._condition

        if arg1 == arg2:
            return Variance(arg1, condition).doit()

        if not arg1.has(RandomSymbol):
            return S.Zero
        if not arg2.has(RandomSymbol):
            return S.Zero

        arg1, arg2 = sorted([arg1, arg2], key=default_sort_key)

        if isinstance(arg1, RandomSymbol) and isinstance(arg2, RandomSymbol):
            return Covariance(arg1, arg2, condition)

        coeff_rv_list1 = self._expand_single_argument(arg1.expand())
        coeff_rv_list2 = self._expand_single_argument(arg2.expand())

        addends = [a*b*Covariance(*sorted([r1, r2], key=default_sort_key), condition=condition)
                   for (a, r1) in coeff_rv_list1 for (b, r2) in coeff_rv_list2]
        return Add(*addends)