def testProperties(self) :
     lj=LennardJones()
     lj.epsilon=2.0
     lj.sigma=2.0
     lj.cutoff=4.0
     lj.shift=0.0
     # here we test energy computation, as testing property access
     # would always work
     self.assertAlmostEqual(lj.computeEnergy(2.0), 0.0)
     self.assertAlmostEqual(lj.computeEnergy(2.0*2.0**(1.0/6.0)), -2.0)
    def testEnergy(self):
        lj=LennardJones(epsilon=2.0, sigma=2.0)

        # root
        self.assertAlmostEqual(lj.computeEnergy(2.0), 0.0)
        self.assertAlmostEqual(lj.computeEnergy(2.0, 0.0, 0.0), 0.0)

        # minimum
        self.assertAlmostEqual(
            lj.computeEnergy(2.0*2.0**(1.0/6.0)), -2.0)
        self.assertAlmostEqual(lj.computeEnergy(0.0, 2.0*2.0**(1.0/6.0), 0.0), -2.0)