Add GPU references and example to docs: first round.

docs/src/building.tex

@@ -48,7 +48,7 @@ work in the expected way. Our advice is first to download the LAPACK tarfile fro
 \href{http://www.netlib.org/lapack}{www.netlib.org/lapack} and install it independently of ATLAS. In this case,
 you need to modify the OPTS and NOOPT definitions for including -fPIC compilation option
 in the make.inc file of the LAPACK library.
-\item[MPI] \cite{MPI2,MPI1} A version of MPI is available on most
+ \item[MPI] \cite{MPI2,MPI1} A version of MPI is available on most
   high-performance computing systems.
  \item[PSBLAS] \cite{PSBLASGUIDE,psblas_00} Parallel Sparse BLAS (PSBLAS) is
   available from
@@ -61,6 +61,18 @@ Please note that the four previous libraries must have Fortran
 interfaces compatible with AMG4PSBLAS; usually this means that they
 should all be built with the same compiler being used for  AMG4PSBLAS.
 
+If you want to use the PSBLAS support for NVIDIA GPUs, you will also
+need:
+\begin{description}
+ \item[PSBLAS-EXT] Parallel Sparse BLAS (PSBLAS) Extensions, 
+  available from
+  \href{https://psctoolkit.github.io/products/psblasext/}{psctoolkit.github.io/products/psblasext/}; version   1.3.0  (or later). 
+ \item[SPGPU] Sparse CUDA kernels for NVIDIA GPUs; available from
+   GitHub, see also
+   \href{https://psctoolkit.github.io/products/psblasext/}{psctoolkit.github.io/products/psblasext/}.
+ \end{description}
+ See also Sec~\ref{sec:gpu-example}.
+ 
 \subsection{Optional third party libraries\label{sec:third-party}}
 
 We provide interfaces to the following third-party software libraries;

docs/src/gettingstarted.tex

@@ -416,6 +416,45 @@ call P%build(A,desc_A,info)
 \end{listing}
 
 
+
+\subsection{GPU example\label{sec:gpu-example}}
+
+The code reported in Figure~\ref{fig:gpu-ex1} shows how to set  up a
+program exploiting the combined GPU capabilities of PSBLAS and
+AMG4PSBLAS.
+\begin{listing}[h!]
+\ifpdf
+\begin{minted}[breaklines=true,bgcolor=bg,fontsize=\small]{fortran}
+! build a one-level RAS with overlap 2 and ILU(0) on the local blocks.
+call P%init('AS',info)
+call P%set('SUB_OVR',2,info)
+call P%build(A,desc_A,info)
+... ...
+! solve Ax=b with preconditioned BiCGSTAB
+  call psb_krylov('BICGSTAB',A,P,b,x,tol,desc_A,info)
+\end{minted}
+\else
+\begin{center}
+\begin{minipage}{.90\textwidth}
+{\small
+\begin{verbatim}
+! build a one-level RAS with overlap 2 and ILU(0) on the local blocks.
+call P%init('AS',info)
+call P%set('SUB_OVR',2,info)
+call P%build(A,desc_A,info)
+... ...
+! solve Ax=b with preconditioned BiCGSTAB
+  call psb_krylov('BICGSTAB',A,P,b,x,tol,desc_A,info)
+\end{verbatim}
+}
+\end{minipage}
+\end{center}
+\fi
+\caption{setup of a one-level Schwarz preconditioner.\label{fig:gpu-ex1}}
+\end{listing}
+
+
+
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