Re: [Libmesh-users] Lagrange factors

[Tobias M. <tob...@un...>]

Hi David,
Thank you for your fast answer. Indeed, I was not aware that in systems_of_equations_ex5 Lagrange multipliers are used as well; but it is only one DOF there as well, isn't?
The problem in my case is that I don't know before, how many DOFs refer to the L (see matrix block sturcture) and how many to the actual problem described by H.
But maybe I need to write a function that separates the parts on my own.
Best,
Tobias

________________________________
Von: David Knezevic [dav...@ak...]
Gesendet: Mittwoch, 11. Oktober 2017 13:03
An: Tobias Möhle
Cc: lib...@li...
Betreff: Re: [Libmesh-users] Lagrange factors

On Wed, Oct 11, 2017 at 5:02 AM, Tobias Möhle <tob...@un...<mailto:tob...@un...>> wrote:
Dear all,
I am trying to extend my current code to add Lagrange multipliers, leading to extra terms that couplet certain DOFs in a fixed range of the grid.
To do so, I added another variable to my system, leading to the system-matrix of block-structure:

/ H L^T \
\ L  0     /
where H is the matrix corresponding to the actual problem and L contains the Lagrange constrains.
Thus, my system.solution contains in the first part the coefficients of the particular solution and in the lower part the Lagrange multipliers themselves.
Now my question: is there some function to extract the Lagrange multipliers and the actual solution vector (dof-based) separately? Or how is it supposed to be done?


I suggest you refer to systems_of_equations_ex5, since that uses a Lagrange multiplier to impose a constraint. Hopefully that answers your question.

David