api: add support for no interp (interp_order=0)

Author: mloubout

devito/types/basic.py

@@ -1067,11 +1067,11 @@ def _evaluate(self, **kwargs):
         """
         mapper = self._grid_map
         subs = mapper.pop('subs', {})
+        io = self.interp_order
         # Average values if at a location not on the Function's grid
-        if not mapper:
+        if not mapper or io == 0:
             return self
 
-        io = self.interp_order
         retval = self.subs({i.subs(subs): self.indices_ref[d]
                             for d, i in mapper.items()})
         if self.is_harmonic:

devito/types/dense.py

@@ -1095,8 +1095,6 @@ def __init_finalize__(self, *args, **kwargs):
         interp_order = kwargs.get('interp_order', 2)
         if not is_integer(interp_order):
             raise TypeError("`interp_order` must be an integer")
-        elif interp_order < 1:
-            raise ValueError("`interp_order` must be >= 2")
         elif interp_order > self._space_order and self._space_order > 1:
             raise ValueError("`interp_order` must be <= `space_order`")
         self._interp_order = interp_order
@@ -1121,7 +1119,7 @@ def _fd_priority(self):
         return 1 if self.staggered.on_node else 2
 
     def _eval_at(self, func):
-        if self.staggered == func.staggered:
+        if self.staggered == func.staggered or self.interp_order == 0:
             return self
 
         mapper = {}

tests/test_differentiable.py

@@ -152,3 +152,15 @@ def test_avg_mode(ndim, io):
     assert sympy.simplify(b_avg.args[0] - expected) == 0
     assert isinstance(b_avg, SafeInv)
     assert b_avg.base == b
+
+
+def test_no_interp():
+    grid = Grid((10, 10))
+    x = grid.dimensions[0]
+    a = Function(name="a", grid=grid, staggered=NODE, interp_order=0)
+    sa = Function(name="as", grid=grid, staggered=x)
+
+    assert a._eval_at(sa) == a
+    assert sa._eval_at(a) == sa._subs(x, x - x.spacing/2)
+    assert (a*sa)._eval_at(sa) == a*sa
+    assert (a + sa)._eval_at(sa) == a + sa