[dune-pdelab] Instationary heat equation

[conf86 at web.de]

Hello,

I want to solve the instationary equation
\partial_t u + a * \laplace u = f

Where and how can I define this factor a? 

When I try this in operator.hh:

 RF a = 1.0;

 RF factor = it->weight()*eg.geometry().integrationElement(it->position());
 for (size_type i=0; i<lfsu.size(); ++i)
	  r.accumulate(lfsu, i, (a * gradu*gradphi[i] - f * phi[i]) * factor);

it doesn't work (sorry, I'm currently not at my office, so I don't remember the exact error message).


Thank you in advance.