Update INSTALL.txt with HIP instructions

Author: pghysels

INSTALL.txt

@@ -138,8 +138,6 @@ the approximate factorizations.
 
 > cmake ../ -DSTRUMPACK_USE_CUDA=ON
 
-Enabled by default, but turned off if CUDA cannot be found.
-
 CMake will look for the CUDA compiler and libraries (cuBLAS and
 cuSOLVER) in the default location or at CUDAToolkit_ROOT, which can be
 set as
@@ -151,6 +149,26 @@ For full GPU support in the distributed memory sparse direct solver,
 one should also compile with support for SLATE, see below.
 
 
+
+HIP (optional)
+===============
+To enable support for HIP in the sparse solver:
+
+> export HIP_DIR=...
+> cmake ../ \
+      -DSTRUMPACK_USE_HIP=ON \
+      -DCMAKE_HIP_ARCHITECTURES=gfx90a \
+      -DCMAKE_CXX_COMPILER=hipcc
+
+In the above, adjust the HIP_DIR, the GPU architecture, and the HIP
+compiler.
+
+For full GPU support in the distributed memory sparse direct solver,
+one should also compile with support for SLATE, with the HIP backend,
+see below.
+
+
+
 SLATE (optional) for GPU accelerated ScaLAPACK
 ==============================================
 SLATE is a modern ScaLAPACK alternative, bringing support for GPU
@@ -162,6 +180,16 @@ Support for SLATE in STRUMPACK can be enabled with for instance:
 >   -DTPL_SLATE_INCLUDE_DIRS="$SLATEHOME/include/;$SLATEHOME/blaspp/include;$SLATEHOME/lapackpp/include" \
 >   -DTPL_SLATE_LIBRARIES="$SLATEHOME/lib/libslate_scalapack_api.so;$SLATEHOME/lib/libslate.so;$SLATEHOME/blaspp/lib/libblaspp.so;$SLATEHOME/lapackpp/lib/liblapackpp.so"
 
+Or if you simply define SLATE_DIR to point to the SLATE and blas++ and
+lapack++ installation directories, STRUMPACK's CMake should find them
+and you do not need to specify TPL_SLATE_INCLUDE_DIRS and
+TPL_SLATE_LIBRARIES.
+
+Note that SLATE requires MPI_THREAD_MULTIPLE. So you need to
+initialize MPI with MPI_Init_thread with the required argument set to
+MPI_THREAD_MULTIPLE.
+
+
 
 ParMETIS and (PT)Scotch (optional)
 ==================================