From f3bfe47728dff9910b5cb5636b0c4ff04665901e Mon Sep 17 00:00:00 2001
From: mloubout <mathias.louboutin@gmail.com>
Date: Thu, 12 Oct 2023 11:19:53 -0400
Subject: [PATCH] api: enforce interpolation radius to be smaller than any
 input space order

---
 devito/operations/interpolators.py | 17 ++++++++++++++++-
 tests/test_interpolation.py        | 13 +++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/devito/operations/interpolators.py b/devito/operations/interpolators.py
index 3d2dcb74660..10d5ce4fbc9 100644
--- a/devito/operations/interpolators.py
+++ b/devito/operations/interpolators.py
@@ -1,11 +1,12 @@
 from abc import ABC, abstractmethod
+from functools import wraps
 
 import sympy
 from cached_property import cached_property
 
 from devito.finite_differences.differentiable import Mul
 from devito.finite_differences.elementary import floor
-from devito.symbolics import retrieve_function_carriers, INT
+from devito.symbolics import retrieve_function_carriers, retrieve_functions, INT
 from devito.tools import as_tuple, flatten
 from devito.types import (ConditionalDimension, Eq, Inc, Evaluable, Symbol,
                           CustomDimension)
@@ -14,6 +15,18 @@
 __all__ = ['LinearInterpolator', 'PrecomputedInterpolator']
 
 
+def check_radius(func):
+    @wraps(func)
+    def wrapper(interp, *args, **kwargs):
+        r = interp.sfunction.r
+        funcs = set(retrieve_functions(args)) - {interp.sfunction}
+        so = min({f.space_order for f in funcs})
+        if so < r:
+            raise ValueError("Space order %d smaller than interpolation r %d" % (so, r))
+        return func(interp, *args, **kwargs)
+    return wrapper
+
+
 class UnevaluatedSparseOperation(sympy.Expr, Evaluable):
 
     """
@@ -209,6 +222,7 @@ def _interp_idx(self, variables, implicit_dims=None):
 
         return idx_subs, temps
 
+    @check_radius
     def interpolate(self, expr, increment=False, self_subs={}, implicit_dims=None):
         """
         Generate equations interpolating an arbitrary expression into ``self``.
@@ -226,6 +240,7 @@ def interpolate(self, expr, increment=False, self_subs={}, implicit_dims=None):
         """
         return Interpolation(expr, increment, implicit_dims, self_subs, self)
 
+    @check_radius
     def inject(self, field, expr, implicit_dims=None):
         """
         Generate equations injecting an arbitrary expression into a field.
diff --git a/tests/test_interpolation.py b/tests/test_interpolation.py
index 97d86c1759f..7d07c39c781 100644
--- a/tests/test_interpolation.py
+++ b/tests/test_interpolation.py
@@ -761,3 +761,16 @@ def test_inject_function():
     for i in [0, 1, 3, 4]:
         for j in [0, 1, 3, 4]:
             assert u.data[1, i, j] == 0
+
+
+def test_interpolation_radius():
+    nt = 11
+
+    grid = Grid(shape=(5, 5))
+    u = TimeFunction(name="u", grid=grid, space_order=0)
+    src = SparseTimeFunction(name="src", grid=grid, nt=nt, npoint=1)
+    try:
+        src.interpolate(u)
+        assert False
+    except ValueError:
+        assert True