Draft: Changes for compatibility with pystencils 2.0

Introduce a significant number of patches for compatibility with the upcoming pystencils 2.0.

Changes

Testing & CI

• Introduce nox to orchestrate environments and testing
• Adapt CI to use nox sessions where applicable
• Remove minimal_conda and ubuntu CI tasks
  • Since the pycodegen/ubuntu docker image is based on a CUDA image, and using a virtual environment for Python, the ubuntu task effectively does the same as the Nox+CUDA task
• Introduce nox session and CI task to test against pystencils/v2.0-dev

Status

• Fix field duplication in create_lb_update_rule: Remove the workaround once field duplication is fixed in pystencils
• Data types in boundary handling: LatticeBoltzmannBoundaryHandling does not allow to specify a data type and always uses float64. This leads to type errors when combined with LB fields with float32 dtype.
• Mixed precision: Need to explicitly insert casts at field reads/writes when computing and storing PDFs in different float formats

src/lbmpy/boundaries/boundaryconditions.py

@@ -147,6 +147,8 @@ class NoSlip(LbBoundary):
             force = sp.Symbol("f")
             subexpressions = [Assignment(force, sp.Float(2.0) * f_out(dir_symbol))]
             offset = NeighbourOffsetArrays.neighbour_offset(dir_symbol, lb_method.stencil)
+            if IS_PYSTENCILS_2:
+                offset = [CastFunc.as_numeric(o) for o in offset]
             for i in range(lb_method.stencil.D):
                 subexpressions.append(Assignment(force_vector[0](f'F_{i}'), force * offset[i]))
         else:
@@ -228,6 +230,8 @@ class NoSlipLinearBouzidi(LbBoundary):
             force = sp.Symbol("f")
             subexpressions.append(Assignment(force, f_xf + rhs))
             offset = NeighbourOffsetArrays.neighbour_offset(dir_symbol, lb_method.stencil)
+            if IS_PYSTENCILS_2:
+                offset = [CastFunc.as_numeric(o) for o in offset]
             for i in range(lb_method.stencil.D):
                 subexpressions.append(Assignment(force_vector[0](f'F_{i}'), force * offset[i]))
 
@@ -382,6 +386,8 @@ class QuadraticBounceBack(LbBoundary):
             force = sp.Symbol("f")
             subexpressions.append(Assignment(force, f_xf + result))
             offset = NeighbourOffsetArrays.neighbour_offset(dir_symbol, lb_method.stencil)
+            if IS_PYSTENCILS_2:
+                offset = [CastFunc.as_numeric(o) for o in offset]
             for i in range(lb_method.stencil.D):
                 subexpressions.append(Assignment(force_vector[0](f'F_{i}'), force * offset[i]))