Revert "GTMGPC: use the new Interpolate"

This reverts commit fd63370.

Author: pbrubeck

firedrake/preconditioners/gtmg.py

@@ -2,11 +2,6 @@
 from firedrake.preconditioners.base import PCBase
 import firedrake.dmhooks as dmhooks
 
-from firedrake.parameters import parameters
-from firedrake.interpolation import Interpolate
-from firedrake.solving_utils import _SNESContext
-from firedrake.matrix_free.operators import ImplicitMatrixContext
-
 
 __all__ = ['GTMGPC']
 
@@ -17,6 +12,11 @@ class GTMGPC(PCBase):
     _prefix = "gt_"
 
     def initialize(self, pc):
+        from firedrake import TestFunction, parameters
+        from firedrake.assemble import get_assembler
+        from firedrake.interpolation import Interpolator
+        from firedrake.solving_utils import _SNESContext
+        from firedrake.matrix_free.operators import ImplicitMatrixContext
 
         _, P = pc.getOperators()
         appctx = self.get_appctx(pc)
@@ -37,7 +37,6 @@ def initialize(self, pc):
 
         # Handle the fine operator if type is python
         if P.getType() == "python":
-            from firedrake.assemble import get_assembler
             ictx = P.getPythonContext()
             if ictx is None:
                 raise ValueError("No context found on matrix")
@@ -103,12 +102,11 @@ def initialize(self, pc):
 
         interp_petscmat = appctx.get("interpolation_matrix", None)
         if interp_petscmat is None:
-            from firedrake.assemble import assemble
             # Create interpolation matrix from coarse space to fine space
             fine_space = ctx.J.arguments()[0].function_space()
-            coarse_test, coarse_trial = coarse_operator.arguments()
-            interp = assemble(Interpolate(coarse_trial, fine_space))
-            interp_petscmat = interp.petscmat
+            interpolator = Interpolator(TestFunction(coarse_space), fine_space)
+            interpolation_matrix = interpolator.callable()
+            interp_petscmat = interpolation_matrix.handle
 
         # We set up a PCMG object that uses the constructed interpolation
         # matrix to generate the restriction/prolongation operators.