Helmholtz brick

This brick represents the complex or real Helmholtz problem:

\Delta u + k^2 u = \ldots

where k the wave number is a real or complex value. For a complex version, a complex model has to be used (see tests/helmholtz.cc).

The function adding a Helmholtz brick to a model is:

getfem::add_Helmholtz_brick(md, mim, varname, dataexpr, region);

where varname is the variable on which the Helmholtz term is added and dataexpr is the wave number.