Merge pull request Pyomo#2896 from michaelbynum/empty_blocks

Make min and max work with MPIBlockVector when some blocks have size 0

pyomo/contrib/pynumero/sparse/mpi_block_vector.py

@@ -567,10 +567,16 @@ def min(self, axis=None, out=None, keepdims=False):
         assert_block_structure(self)
         local_min = np.inf
         for i in self._owned_blocks:
-            lmin = self._block_vector.get_block(i).min()
-            if lmin <= local_min:
-                local_min = lmin
-        return self._mpiw.allreduce(local_min, op=mpi4py.MPI.MIN)
+            block = self._block_vector.get_block(i)
+            if block.size > 0:
+                lmin = block.min()
+                if lmin <= local_min:
+                    local_min = lmin
+        res = self._mpiw.allreduce(local_min, op=mpi4py.MPI.MIN)
+        if res == np.inf:
+            if self.size == 0:
+                raise ValueError('cannot get the min of a size 0 array')
+        return res
 
     def max(self, axis=None, out=None, keepdims=False):
         """
@@ -580,10 +586,16 @@ def max(self, axis=None, out=None, keepdims=False):
         assert_block_structure(self)
         local_max = -np.inf
         for i in self._owned_blocks:
-            lmax = self._block_vector.get_block(i).max()
-            if lmax >= local_max:
-                local_max = lmax
-        return self._mpiw.allreduce(local_max, op=mpi4py.MPI.MAX)
+            block = self._block_vector.get_block(i)
+            if block.size > 0:
+                lmax = block.max()
+                if lmax >= local_max:
+                    local_max = lmax
+        res = self._mpiw.allreduce(local_max, op=mpi4py.MPI.MAX)
+        if res == -np.inf:
+            if self.size == 0:
+                raise ValueError('cannot get the max of a size 0 array')
+        return res
 
     def sum(self, axis=None, dtype=None, out=None, keepdims=False):
         """

pyomo/contrib/pynumero/sparse/tests/test_mpi_block_vector.py

@@ -169,6 +169,35 @@ def test_min(self):
         self.assertEqual(self.v1.min(), 0.0)
         self.assertEqual(self.v2.min(), 0.0)
 
+    def test_min_max_with_size0_blocks(self):
+        v = MPIBlockVector(3, [0, 1, 2], comm)
+        rank = comm.Get_rank()
+        if rank == 0:
+            v.set_block(0, np.array([8, 4, 7, 12]))
+        if rank == 1:
+            v.set_block(1, np.array([]))
+        if rank == 2:
+            v.set_block(2, np.array([5, 6, 3]))
+        self.assertAlmostEqual(v.min(), 3)
+        self.assertAlmostEqual(v.max(), 12)
+
+        if rank == 0:
+            v.set_block(0, np.array([np.inf, np.inf, np.inf, np.inf]))
+        if rank == 2:
+            v.set_block(2, np.array([np.inf, np.inf, np.inf]))
+        self.assertEqual(v.min(), np.inf)
+        self.assertEqual(v.max(), np.inf)
+        v *= -1
+        self.assertEqual(v.min(), -np.inf)
+        self.assertEqual(v.max(), -np.inf)
+
+        v = MPIBlockVector(3, [0, 1, 2], comm)
+        v.set_block(rank, np.array([]))
+        with self.assertRaisesRegex(ValueError, 'cannot get the min of a size 0 array'):
+            v.min()
+        with self.assertRaisesRegex(ValueError, 'cannot get the max of a size 0 array'):
+            v.max()
+
     def test_max(self):
         v = MPIBlockVector(2, [0, 1], comm)
         rank = comm.Get_rank()