[attachment=undefined]eigen_prob.png[/attachment]Hi ngsolve comminity,

I would like to calculate the element-wise eigenvalue k of an generalized eigenvalue problem in the case “CufFEM” or X-FEM.

The problem is stated as:

A[sub]m[/sub] x=k[sub]e,m[/sub]B[sub]m[/sub]x

where the matrix A and B is written as attached figure

[attachment=undefined]eigen_prob.png[/attachment]

Could you give some instruction on implementing this problem, I tried something to calculte the integrator like:

```
lsPOS = {"levelset": levelset, "domain_type": POS}
lsNEG = {"levelset": levelset, "domain_type": NEG}
lsIF = {"levelset": levelset, "domain_type": IF}
space_flux = HDiv(mesh, order=2)
f = GridFunction(space_flux, "flux")
flux = grad(f)
#intf = Integrate(lsPOS, mesh=mesh, cf=flux, element_wise=True)
intf = Integrate(lsNEG, mesh=mesh, cf=flux, element_wise=True)
intf = Integrate(lsIF, mesh=mesh, cf=flux, element_wise=True)
intf = Integrate(flux, mesh, VOL, element_wise=True)
```

I am not sure if I do this with function Integrate or with symbolic integrators

Then with the computed integrator, How can we calculate the eigenvalue problem? I saw some demos which use the algrhitome like PINVIT?