Fix error in 3D quintic spline factor.

Somehow this was set to 3/359 and not 1/120.  This is now fixed as per
many refernces including Violeau's book.

pysph/base/kernels.py

@@ -1064,7 +1064,7 @@ class QuinticSpline(object):
     .. math::
              \sigma_5  = \ & \frac{1}{120 h^1}, & \textrm{for dim=1}, \\
              \sigma_5  = \ & \frac{7}{478\pi h^2}, \ & \textrm{for dim=2}, \\
-             \sigma_5  = \ & \frac{3}{359\pi h^3}, & \textrm{for dim=3}. \\
+             \sigma_5  = \ & \frac{1}{120\pi h^3}, & \textrm{for dim=3}. \\
 
     """
 
@@ -1077,7 +1077,7 @@ def __init__(self, dim=2):
         elif dim == 2:
             self.fac = M_1_PI * 7.0 / 478.0
         elif dim == 3:
-            self.fac = M_1_PI * 3.0 / 359.0
+            self.fac = M_1_PI * 1.0 / 120.0
 
     def get_deltap(self):
         # The inflection points for the polynomial are obtained as

pysph/base/tests/test_kernel.py

@@ -354,7 +354,7 @@ class TestQuinticSpline3D(TestGaussian3D):
     kernel_factory = staticmethod(lambda: QuinticSpline(dim=3))
 
     def test_simple(self):
-        self.check_kernel_at_origin(66.0 * 3.0 / (359.0 * np.pi))
+        self.check_kernel_at_origin(66.0 * 1.0 / (120.0 * np.pi))
 
 
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