a better implementation of SparseType.may_share_memory. test it.

theano/sparse/basic.py

@@ -190,7 +190,18 @@ class SparseType(gof.Type):
     def may_share_memory(a,b):
         # This is Fred suggestion for a quick and dirty way of checking
         # aliasing .. this can potentially be further refined (ticket #374)
-        return a is b
+        if _is_sparse(a) and _is_sparse(b):
+            return a is b
+        if _is_sparse(b) and isinstance(a, numpy.ndarray):
+            a,b=b,a
+        if _is_sparse(a) and isinstance(b, numpy.ndarray):
+            if (numpy.may_share_memory(a.data,b) or
+                numpy.may_share_memory(a.indices,b) or
+                numpy.may_share_memory(a.indptr,b)):
+                    #currently we can't share memory with a.shape as it is a tuple
+                return True
+        return False
+
 
     def make_variable(self, name = None):
         return SparseVariable(self, name = name)
@@ -250,7 +261,7 @@ class _sparse_py_operators:
     def __rdot__(right, left): return structured_dot(left, right)
 
     #N.B. THIS IS COMMENTED OUT ON PURPOSE!!!
-    #     Discussion with Fred & James (at least, and maybe others before) 
+    #     Discussion with Fred & James (at least, and maybe others before)
     #     we decided that casting from a sparse to dense should be explicit
     #     because it's usually something you want to be pretty careful about,
     #     and not to do by accident.

theano/sparse/tests/test_basic.py

@@ -485,6 +485,20 @@ def test_shape():
         assert isinstance(topo[1].op,tensor.opt.Shape_i)
         assert isinstance(topo[2].op,tensor.opt.MakeVector)
 
+def test_may_share_memory():
+    a=scipy.sparse.csc_matrix(scipy.sparse.eye(5,3))
+    b=scipy.sparse.csc_matrix(scipy.sparse.eye(4,3))
+    as_ar = lambda a: theano._asarray(a, dtype='int32')
+    for a_,b_,rep in [(a,a,True),(b,b,True),(a,b,False),
+                    (a,a.data,True),(a,a.indptr,True),(a,a.indices,True),(a,as_ar(a.shape),False),
+                    (a.data,a,True),(a.indptr,a,True),(a.indices,a,True),(as_ar(a.shape),a,False),
+                    (b,b.data,True),(b,b.indptr,True),(b,b.indices,True),(b,as_ar(b.shape),False),
+                    (b.data,b,True),(b.indptr,b,True),(b.indices,b,True),(as_ar(b.shape),b,False),
+                    (b.data,a,False),(b.indptr,a,False),(b.indices,a,False),(as_ar(b.shape),a,False),
+                    ]:
+
+        assert SparseType.may_share_memory(a_,b_)==rep
+
 import theano.tensor.tests.test_sharedvar
 test_shared_options=theano.tensor.tests.test_sharedvar.makeSharedTester(
     theano.sparse.shared, 'float64',