try cos, sin functions instead of variables

Author: isuruf

sumpy/kernel.py

@@ -28,6 +28,7 @@
 from sumpy.symbolic import pymbolic_real_norm_2, SpatialConstant
 import sumpy.symbolic as sym
 from pymbolic.primitives import make_sym_vector
+import pymbolic.primitives as prim
 from pymbolic import var
 from pytools import memoize_method
 from collections import defaultdict
@@ -522,7 +523,7 @@ def __init__(self, dim, helmholtz_k_name="k",
             if allow_evanescent:
                 expr = var("exp")(var("I")*k*r)/r
             else:
-                expr = (var("cos")(k*r) + var("I")*var("sin")(k*r))/r
+                expr = (prim.cos(k*r) + var("I")*prim.sin(k*r))/r
             scaling = 1/(4*var("pi"))
         else:
             raise RuntimeError("unsupported dimensionality")