Print warnings when not running on GPU

src/SparseSolver.cpp

@@ -293,6 +293,17 @@ namespace strumpack {
     auto MFsolve =
       [&](scalar_t* w) {
         DenseMW_t X(x.rows(), 1, w, x.ld());
+#if !defined(STRUMPACK_USE_MAGMA)
+        if (opts_.use_gpu())
+          std::cerr
+            << "-------------------------------------------------------" << std::endl
+            << "WARNING: sparse multifrontal solve is done on CPU," << std::endl
+            << "GPU solve requires MAGMA, see" << std::endl
+            << "   https://bitbucket.org/icl/magma/src/master/" << std::endl
+            << "Configure with -DTPL_ENABLE_MAGMA=ON" << std::endl
+            << "and set the MAGMA_DIR environment variable" << std::endl
+            << "-------------------------------------------------------" << std::endl
+#endif
         tree()->multifrontal_solve(X);
       };
 

src/SparseSolverMPIDist.cpp

@@ -57,13 +57,20 @@ namespace strumpack {
 #if defined(STRUMPACK_USE_SLATE_SCALAPACK)
     int thread_level;
     MPI_Query_thread(&thread_level);
-    if (thread_level != MPI_THREAD_MULTIPLE &&
-        mpi_rank(comm) == 0)
+    if (thread_level != MPI_THREAD_MULTIPLE && !mpi_rank(comm))
       std::cerr << "MPI_THREAD_MULTIPLE is required for SLATE"
                 << std::endl;
+#else
+    if (opts_.use_gpu() && !mpi_rank(comm))
+      std::cerr
+        << "-------------------------------------------------------" << std::endl
+        << "WARNING: SLATE is required for full GPU support." << std::endl
+        << "SLATE is a GPU-capable replacement for ScaLAPACK, see" << std::endl
+        << "   https://github.com/icl-utk-edu/slate" << std::endl
+        << "Configure with -DTPL_ENABLE_SLATE=ON" << std::endl
+        << "and set the SLATE_DIR environment variable." << std::endl
+        << "-------------------------------------------------------" << std::endl;
 #endif
-    // Set the default reordering to PARMETIS?
-    //opts_.set_reordering_method(ReorderingStrategy::PARMETIS);
   }
 
   template<typename scalar_t,typename integer_t> MPI_Comm

src/sparse/fronts/FrontMAGMA.cpp

@@ -803,8 +803,12 @@ namespace strumpack {
   FrontMAGMA<scalar_t,integer_t>::multifrontal_solve
   (DenseM_t& b) const {
     if (dev_factors_) gpu_solve(b);
-    else // factors are not on the device, solve on CPU
+    else {
+      if (!mpi_rank())
+        std::cerr << "WARNING: Solve is performed on CPU" << std::endl;
+      // factors are not on the device, solve on CPU
       FrontalMatrix<scalar_t,integer_t>::multifrontal_solve(b);
+    }
   }
 
   template<typename scalar_t,typename integer_t> void