This brick represents the complex or real Helmholtz problem:
where 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.