Merge branch 'fix_mpi_gather_scatter' into 'master'

Fix mpi gather scatter

See merge request !885

(cherry picked from commit 6c31280e)

ab926cb1 fix igather and iscatter in mpicommunication
b2bafd86 add missing includes and fix initialization of array in mpigatherscattertest

dune/common/parallel/mpicommunication.hh

@@ -307,12 +307,12 @@ namespace Dune
 
     //! @copydoc Communication::igather
     template<class TIN, class TOUT = std::vector<TIN>>
-    MPIFuture<TOUT, TIN> igather(TIN&& data_in, TOUT&& data_out, int root){
+    MPIFuture<TOUT, TIN> igather(TIN&& data_in, TOUT&& data_out, int root) const{
       MPIFuture<TOUT, TIN> future(std::forward<TOUT>(data_out), std::forward<TIN>(data_in));
       auto mpidata_in = future.get_send_mpidata();
       auto mpidata_out = future.get_mpidata();
       assert(root != me || mpidata_in.size()*procs <= mpidata_out.size());
-      int outlen = me==root * mpidata_in.size();
+      int outlen = (me==root) * mpidata_in.size();
       MPI_Igather(mpidata_in.ptr(), mpidata_in.size(), mpidata_in.type(),
                   mpidata_out.ptr(), outlen, mpidata_out.type(),
                   root, communicator, &future.req_);
@@ -345,7 +345,7 @@ namespace Dune
       MPIFuture<TOUT, TIN> future(std::forward<TOUT>(data_out), std::forward<TIN>(data_in));
       auto mpidata_in = future.get_send_mpidata();
       auto mpidata_out = future.get_mpidata();
-      int inlen = me==root * mpidata_in.size();
+      int inlen = (me==root) * mpidata_in.size()/procs;
       MPI_Iscatter(mpidata_in.ptr(), inlen, mpidata_in.type(),
                   mpidata_out.ptr(), mpidata_out.size(), mpidata_out.type(),
                   root, communicator, &future.req_);

dune/common/parallel/test/CMakeLists.txt

@@ -44,3 +44,10 @@ dune_add_test(SOURCES mpipacktest.cc
               TIMEOUT 300
               CMAKE_GUARD MPI_FOUND
               LABELS quick)
+
+dune_add_test(SOURCES mpigatherscattertest.cc
+              LINK_LIBRARIES dunecommon
+              MPI_RANKS 2
+              TIMEOUT 300
+              CMAKE_GUARD MPI_FOUND
+              LABELS quick)

dune/common/parallel/test/mpigatherscattertest.cc

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+
+#include <config.h>
+
+#include <iostream>
+#include <array>
+#include <vector>
+
+
+#include <dune/common/parallel/mpihelper.hh>
+#include <dune/common/parallel/mpicommunication.hh>
+#include <dune/common/exceptions.hh>
+
+using namespace Dune;
+
+int main(int argc, char** argv){
+  MPIHelper & mpihelper = MPIHelper::instance(argc, argv);
+  auto cc = mpihelper.getCommunication();
+  int rank = cc.rank();
+  int size = cc.size();
+
+  std::array<double, 2> data = {1.0 + rank, 2.0 + rank};
+
+  auto gathered = cc.igather(data, std::vector<double>(rank==0?2*size:0), 0).get();
+
+  for(auto& d : gathered)
+    d += 1;
+
+  cc.iscatter(gathered, data, 0).get();
+  if(data[0] != 2+rank ||
+     data[1] != 3+rank){
+    DUNE_THROW(Exception, "Wrong result after gather - scatter");
+  }
+
+  return 0;
+}