def _reverse_input_einsum_eq(equation):
    """
    Reverse the input order of the einsum eqaution
    e.g.:
    input : "nchw,nwhu->nchu"
    returns : "nwhu,nchw->nchu"
    """
    input_output_strings = equation.split('->')
    assert len(input_output_strings) == 2, "invalid equation"
    input_strings = input_output_strings[0].split(',')
    assert len(input_strings) == 2, "invalid equation"
    equation = input_strings[1] + ',' + input_strings[0] + '->' + input_output_strings[1]
    return equation