From 7bd4e6788200eca9a8e4a35802ae129bc456dbee Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <inform@tiker.net>
Date: Mon, 4 Jan 2016 00:06:07 -0600
Subject: [PATCH] Add is_surjective flag to mesh connections

---
 meshmode/discretization/connection/__init__.py     | 14 ++++++++++++--
 meshmode/discretization/connection/face.py         |  3 ++-
 .../discretization/connection/opposite_face.py     |  3 ++-
 meshmode/discretization/connection/same_mesh.py    |  3 ++-
 4 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/meshmode/discretization/connection/__init__.py b/meshmode/discretization/connection/__init__.py
index dcfcd5e3..fcb6cc69 100644
--- a/meshmode/discretization/connection/__init__.py
+++ b/meshmode/discretization/connection/__init__.py
@@ -164,13 +164,18 @@ class DiscretizationConnection(object):
         instances, with a one-to-one correspondence to the groups in
         :attr:`to_discr`.
 
+    .. attribute:: is_surjective
+
+        A :class:`bool` indicating whether every output degree
+        of freedom is set by the connection.
+
     .. automethod:: __call__
 
     .. automethod:: full_resample_matrix
 
     """
 
-    def __init__(self, from_discr, to_discr, groups):
+    def __init__(self, from_discr, to_discr, groups, is_surjective):
         if from_discr.cl_context != to_discr.cl_context:
             raise ValueError("from_discr and to_discr must live in the "
                     "same OpenCL context")
@@ -191,6 +196,8 @@ class DiscretizationConnection(object):
         self.to_discr = to_discr
         self.groups = groups
 
+        self.is_surjective = is_surjective
+
     @memoize_method
     def _resample_matrix(self, to_group_index, ibatch_index):
         import modepy as mp
@@ -356,7 +363,10 @@ class DiscretizationConnection(object):
         if not isinstance(vec, cl.array.Array):
             return vec
 
-        result = self.to_discr.empty(dtype=vec.dtype)
+        if self.is_surjective:
+            result = self.to_discr.empty(dtype=vec.dtype)
+        else:
+            result = self.to_discr.zeros(dtype=vec.dtype)
 
         if vec.shape != (self.from_discr.nnodes,):
             raise ValueError("invalid shape of incoming resampling data")
diff --git a/meshmode/discretization/connection/face.py b/meshmode/discretization/connection/face.py
index f847e5da..521dd056 100644
--- a/meshmode/discretization/connection/face.py
+++ b/meshmode/discretization/connection/face.py
@@ -81,7 +81,8 @@ def _build_boundary_connection(queue, vol_discr, bdry_discr, connection_data):
                     connection_batches))
 
     return DiscretizationConnection(
-            vol_discr, bdry_discr, connection_groups)
+            vol_discr, bdry_discr, connection_groups,
+            is_surjective=True)
 
 # }}}
 
diff --git a/meshmode/discretization/connection/opposite_face.py b/meshmode/discretization/connection/opposite_face.py
index 7c0cef52..b7b92aba 100644
--- a/meshmode/discretization/connection/opposite_face.py
+++ b/meshmode/discretization/connection/opposite_face.py
@@ -383,7 +383,8 @@ def make_opposite_face_connection(volume_to_bdry_conn):
             to_discr=bdry_discr,
             groups=[
                 DiscretizationConnectionElementGroup(batches=batches)
-                for batches in groups])
+                for batches in groups],
+            is_surjective=True)
 
 # }}}
 
diff --git a/meshmode/discretization/connection/same_mesh.py b/meshmode/discretization/connection/same_mesh.py
index 7f07f598..3b73e34f 100644
--- a/meshmode/discretization/connection/same_mesh.py
+++ b/meshmode/discretization/connection/same_mesh.py
@@ -57,7 +57,8 @@ def make_same_mesh_connection(to_discr, from_discr):
                     DiscretizationConnectionElementGroup([ibatch]))
 
     return DiscretizationConnection(
-            from_discr, to_discr, groups)
+            from_discr, to_discr, groups,
+            is_surjective=True)
 
 # }}}
 
-- 
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