trace.py 文件源码

def permute(self, pos):
        """ Permute the arguments cyclically.

        Parameters
        ==========
        pos : integer, if positive, shift-right, else shift-left

        Examples
        ========

        >>> from sympy.core.trace import Tr
        >>> from sympy import symbols
        >>> A, B, C, D = symbols('A B C D', commutative=False)
        >>> t = Tr(A*B*C*D)
        >>> t.permute(2)
        Tr(C*D*A*B)
        >>> t.permute(-2)
        Tr(C*D*A*B)

        """
        if pos > 0:
            pos = pos % len(self.args[0].args)
        else:
            pos = -(abs(pos) % len(self.args[0].args))

        args = list(self.args[0].args[-pos:] + self.args[0].args[0:-pos])

        return Tr(Mul(*(args)))