%Doing many experiments with many cores is not easy and requires to access to a supercomputer with several hours for developing a code and then improving it.
In the following we present some experiments we could achieved out on the Hector
-architecture, a UK's high-end computing resource, funded by the UK
-Research Councils. This is a Cray XE6 supercomputer, equipped with two 16-core
-AMD Opteron 2.3 Ghz and 32 GB of memory. Machines are interconnected with a 3D
-torus.
+architecture, a UK's high-end computing resource, funded by the UK Research
+Councils~\cite{hector}. This is a Cray XE6 supercomputer, equipped with two
+16-core AMD Opteron 2.3 Ghz and 32 GB of memory. Machines are interconnected
+with a 3D torus.
Table~\ref{tab1} shows the result of the experiments. The first column shows
the size of the 3D Poisson problem. The size is chosen in order to have
