Trilinos parallel is_non_negative() function

doc/news/changes/minor/20211202OConnor

@@ -0,0 +1,4 @@
+Changed: The function TrilinosWrappers::Vector::is_non_negative() now also works in parallel.
+<br>
+(Justin O'Connor, 2021/12/02)
+

source/lac/trilinos_vector.cc

@@ -757,36 +757,26 @@ namespace TrilinosWrappers
     bool
     Vector::is_non_negative() const
     {
-      // if this vector is a parallel one, then
-      // we need to communicate to determine
-      // the answer to the current
-      // function. this still has to be
-      // implemented
-      AssertThrow(local_size() == size(), ExcNotImplemented());
       // get a representation of the vector and
       // loop over all the elements
-      TrilinosScalar *start_ptr;
-      int             leading_dimension;
-      int ierr = vector->ExtractView(&start_ptr, &leading_dimension);
-      AssertThrow(ierr == 0, ExcTrilinosError(ierr));
-
-      // TODO: This
-      // won't work in parallel like
-      // this. Find out a better way to
-      // this in that case.
-      const TrilinosScalar *ptr = start_ptr, *eptr = start_ptr + size();
-      bool                  flag = true;
+      TrilinosScalar *      start_ptr = (*vector)[0];
+      const TrilinosScalar *ptr = start_ptr, *eptr = start_ptr + local_size();
+      unsigned int          flag = 0;
       while (ptr != eptr)
         {
           if (*ptr < 0.0)
             {
-              flag = false;
+              flag = 1;
               break;
             }
           ++ptr;
         }
 
-      return flag;
+      // in parallel, check that the vector
+      // is zero on _all_ processors.
+      const auto max_n_negative =
+        Utilities::MPI::max(flag, get_mpi_communicator());
+      return max_n_negative == 0;
     }
 
 

tests/mpi/trilinos_vector_non_negative.cc

@@ -0,0 +1,92 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2011 - 2020 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE.md at
+// the top level directory of deal.II.
+//
+// ---------------------------------------------------------------------
+
+
+
+// check correct behavior of checking all Trilinos vector entries are
+// non-negative works for distributed vectors
+
+#include <deal.II/base/index_set.h>
+#include <deal.II/base/utilities.h>
+
+#include <deal.II/lac/trilinos_vector.h>
+
+#include <iostream>
+#include <vector>
+
+#include "../tests.h"
+
+
+void
+test()
+{
+  const unsigned int myid = Utilities::MPI::this_mpi_process(MPI_COMM_WORLD);
+  const unsigned int n_processes =
+    Utilities::MPI::n_mpi_processes(MPI_COMM_WORLD);
+
+  // create a vector that consists of elements indexed from 0 to n
+  TrilinosWrappers::MPI::Vector vec;
+  {
+    IndexSet is(100 * n_processes);
+    is.add_range(100 * myid, 100 * myid + 100);
+    vec.reinit(is, MPI_COMM_WORLD);
+  }
+  AssertThrow(vec.local_size() == 100, ExcInternalError());
+  AssertThrow(vec.local_range().first == 100 * myid, ExcInternalError());
+  AssertThrow(vec.local_range().second == 100 * myid + 100, ExcInternalError());
+  for (unsigned int i = vec.local_range().first; i < vec.local_range().second;
+       ++i)
+    vec(i) = i;
+  vec.compress(VectorOperation::insert);
+
+  // verify correctness so far
+  {
+    bool exact_non_negative = true;
+    AssertThrow(vec.is_non_negative() == exact_non_negative,
+                ExcInternalError());
+  }
+
+  if (vec.in_local_range(vec.size() / 2))
+    vec[vec.size() / 2] = -1;
+  {
+    bool exact_non_negative = false;
+    AssertThrow(vec.is_non_negative() == exact_non_negative,
+                ExcInternalError());
+  }
+
+  deallog << "OK" << std::endl;
+}
+
+
+
+int
+main(int argc, char **argv)
+{
+  Utilities::MPI::MPI_InitFinalize mpi_initialization(argc, argv, 1);
+
+  unsigned int myid = Utilities::MPI::this_mpi_process(MPI_COMM_WORLD);
+
+
+  deallog.push(Utilities::int_to_string(myid));
+
+  if (myid == 0)
+    {
+      initlog();
+
+      test();
+    }
+  else
+    test();
+}

tests/mpi/trilinos_vector_non_negative.with_trilinos=true.mpirun=2.output

@@ -0,0 +1,2 @@
+
+DEAL:0::OK