def evals(_x, _params):
    """Eigenvalues of the linearized equations of motion about the upright
configuration with spin rate treated as a parameter.

    """
    # Unpack function arguments
    u2 = _x

    # Unpack function parameters
    g, r = _params

    # Calculate return values
    ev1 = 5**(1/2)*(4*g/r - 12*u2**2)**(1/2)/5
    ev2 = -5**(1/2)*(4*g/r - 12*u2**2)**(1/2)/5
    ev3 = 0

    # Return calculated values
    return [ev1, ev2, ev3]