diff --git a/hysop/__init__.py b/hysop/__init__.py
index c7837446ab5ddc747c7b39a06f83a72361073be9..3d858751360fa2b672c80e971cf6a117ef995fc6 100644
--- a/hysop/__init__.py
+++ b/hysop/__init__.py
@@ -45,8 +45,8 @@ __TEST_ALL_OPENCL_PLATFORMS__ = get_env('TEST_ALL_OPENCL_PLATFORMS', False)
 __ENABLE_LONG_TESTS__ = get_env('ENABLE_LONG_TESTS', ("OFF" is "ON"))
 
 # OpenCL
-__DEFAULT_PLATFORM_ID__ = 0
-__DEFAULT_DEVICE_ID__   = 0
+__DEFAULT_PLATFORM_ID__ = get_env('DEFAULT_PLATFORM_ID', 0)
+__DEFAULT_DEVICE_ID__   = get_env('DEFAULT_DEVICE_ID', 0)
 
 
 if __MPI_ENABLED__:
diff --git a/hysop/__init__.py.in b/hysop/__init__.py.in
index 4e9ba6b3f9b066da41ca9643630b0feccb88be5a..8037731957abe6e93d8225e8b3f5d1a977e2f486 100644
--- a/hysop/__init__.py.in
+++ b/hysop/__init__.py.in
@@ -45,8 +45,8 @@ __TEST_ALL_OPENCL_PLATFORMS__ = get_env('TEST_ALL_OPENCL_PLATFORMS', False)
 __ENABLE_LONG_TESTS__ = get_env('ENABLE_LONG_TESTS', ("@ENABLE_LONG_TESTS@" is "ON"))
 
 # OpenCL
-__DEFAULT_PLATFORM_ID__ = @OPENCL_DEFAULT_OPENCL_PLATFORM_ID@
-__DEFAULT_DEVICE_ID__   = @OPENCL_DEFAULT_OPENCL_DEVICE_ID@
+__DEFAULT_PLATFORM_ID__ = get_env('DEFAULT_PLATFORM_ID', @OPENCL_DEFAULT_OPENCL_PLATFORM_ID@)
+__DEFAULT_DEVICE_ID__   = get_env('DEFAULT_DEVICE_ID', @OPENCL_DEFAULT_OPENCL_DEVICE_ID@)
 
 if __MPI_ENABLED__:
     from hysop.core.mpi import MPI, main_rank, main_size, \
diff --git a/hysop/backend/device/codegen/symbolic/functions/apply_stencil.py b/hysop/backend/device/codegen/symbolic/functions/apply_stencil.py
index aec9251825fea3f43308b62f09317d3a62c6b2e6..6291d7fcb41b66f4f25272da00f40e6b4a621305 100644
--- a/hysop/backend/device/codegen/symbolic/functions/apply_stencil.py
+++ b/hysop/backend/device/codegen/symbolic/functions/apply_stencil.py
@@ -13,7 +13,7 @@ from hysop.backend.device.codegen.symbolic.expr import OpenClPrinter, Return, Nu
 from hysop.symbolic.misc import ApplyStencil
 
 from hysop.backend.device.codegen.symbolic.expr import FunctionCall, OpenClVariable
-from hysop.backend.device.codegen.symbolic.ops import Mul, Add, Pow
+from hysop.backend.device.codegen.symbolic.relational import OpenClMul, OpenClAdd
 
 class CustomApplyStencilFunction(CustomSymbolicFunction):
     def __init__(self, csc, name, expr, target_ctype=None, **kwds):
@@ -33,9 +33,9 @@ class CustomApplyStencilFunction(CustomSymbolicFunction):
             factor = self.parse_expr(csc, name, stencil.factor, args, reqs)
             pexprs = ()
             for (i, coeff) in stencil.iteritems(include_factor=False):
-                pexprs += (Mul(fn.ctype, NumericalConstant.build(coeff, csc.typegen), fn_call(i[0], fn_kwds)),)
-            pexpr  = Add(fn.ctype, *pexprs)
-            pexpr  = Mul(fn.ctype, factor, pexpr)
+                pexprs += (OpenClMul(fn.ctype, NumericalConstant.build(coeff, csc.typegen), fn_call(i[0], fn_kwds)),)
+            pexpr  = OpenClAdd(fn.ctype, *pexprs)
+            pexpr  = OpenClMul(fn.ctype, factor, pexpr)
         else:
             pexpr = super(CustomApplyStencilFunction, self).parse_expr(csc, name, expr, args, reqs)
         return pexpr