diff --git a/src/sage/combinat/alternating_sign_matrix.py b/src/sage/combinat/alternating_sign_matrix.py index cb10e8c6a22..118d8a4e076 100644 --- a/src/sage/combinat/alternating_sign_matrix.py +++ b/src/sage/combinat/alternating_sign_matrix.py @@ -286,6 +286,27 @@ def rotate_ccw(self): l.reverse() return AlternatingSignMatrix(matrix(l)) + def inversion_number(self): + r""" + Return the inversion number of ``self``. + + EXAMPLES:: + + sage: A = AlternatingSignMatrices(3) + sage: A([[1, 0, 0],[0, 1, 0],[0, 0, 1]]).inversion_number() + 0 + sage: asm = A([[0, 0, 1],[1, 0, 0],[0, 1, 0]]) + sage: asm.inversion_number() + 2 + """ + inversion_num = 0 + asm_matrix = self.to_matrix() + for (i,j) in asm_matrix.nonzero_positions(): + for (k,l) in asm_matrix.nonzero_positions(): + if i>k and j