[eigen] request to add Lancroz and LOBPCG methods

[marco stamazza]

Hi,
as always, thanks for the great work.

I wanted to ask if there are plans to implement efficient eigensolvers,
such as Lancroz and LOBPCG, for example.

It would be nice in a library called eigen!

Thanks, Marco

ps I don't suggest I start it because of lack of programmng skills
ps2 tried with eigen-request but it was bounced back