def index(self):
        """
        Returns the index of a permutation.

        The index of a permutation is the sum of all subscripts j such
        that p[j] is greater than p[j+1].

        Examples
        ========

        >>> from sympy.combinatorics.permutations import Permutation
        >>> p = Permutation([3, 0, 2, 1, 4])
        >>> p.index()
        2
        """
        a = self.array_form

        return sum([j for j in range(len(a) - 1) if a[j] > a[j + 1]])
dataset/ETHPy150Open sympy/sympy/sympy/combinatorics/permutations.py/Permutation.index/original