Solving a linear system

int main(int argc, char**argv )
{
    // initialize feel++
    using namespace Feel;
    Environment env( _argc=argc, _argv=argv,
                     _about=about(_name="mylaplacian",
                                  _author="Feel++ Consortium",
                                  _email="feelpp-devel@feelpp.org"));
    // create mesh
    auto mesh = unitSquare();

    // function space
    auto Vh = Pch<1>( mesh );
    auto u = Vh->element();
    auto v = Vh->element();

    // left hand side
    auto a = form2( _trial=Vh, _test=Vh );
    a = integrate(_range=elements(mesh),
                  _expr=gradt(u)*trans(grad(v)) );

    // right hand side
    auto l = form1( _test=Vh );
    l = integrate(_range=elements(mesh),
                  _expr=id(v));

    // tagB::marker_on[]
    // apply the boundary condition
    a+=on(_range=boundaryfaces(mesh), _rhs=l, _element=u,
          _expr=expr(soption("functions.alpha")) );

    // solve the equation \f$ a(u,v) = l(v) \f$
    a.solve(_rhs=l,_solution=u);
    // end:marker_solve[]

    // export results
    auto e = exporter( _mesh=mesh );
    e->add( "u", u );
    e->save();
}

# sequential
./feelpp_tut_laplacian
# parallel on 4 cores
mpirun -np 4 ./feelpp_tut_laplacian