def symbolic_e_dcm(axis='z', angle=None):
    """Make elementary matrix that rotate axes, not vectors (sympy)"""
    import sympy
    axis = axis.strip().lower()
    if angle is None:
        angle = sympy.Symbol('x')
    if axis == 'x':
        ret = sympy.rot_axis1(angle)
    elif axis == 'y':
        ret = sympy.rot_axis2(angle)
    elif axis == 'z':
        ret = sympy.rot_axis3(angle)
    else:
        raise ValueError("Unrecognized axis: '{0}'".format(axis))
    return ret
