def testrelat1(self):
     r=g.cos(0)
     self.assertEqual(r,1)
     self.assertNotEqual(r,1.1)
     r=g.cos(g.Pi)
     self.assertEqual(r,-1)
     self.assertNotEqual(r,-2)
     r=g.cos(2*g.Pi)
     self.assertEqual(r,1)
     self.assertNotEqual(r,1.1)
def cos(e):
    return Expr(_g.cos(e()), e.spatial_symbs, time=e.time)