code rewritten with p_arpack.
compilation is ok, but a problem arise with eigenvectors added to the list after parpack call.
Some NaN appear in the eigenvector, probably due to some bugs in the H*v routine.
MPI code working. Using P_Arpack interface.
Previous bug fixed: a memory problem arose bcast-ing the eigenvector inside the p_arpack interface, as
the 2d array evec (output of the routine) was not init to zero, and evec_tmp as well.
Correct initialization to zero fixed the bug.
Go on with some speed scaling, that does not look promising.