Re: [Getfem-users] Maximum allowed residuum

[Yves Renard]

Dear Jena,

Unfortunately, from the interface you cannot adjust the maximum residual and 
change it from a Newton sub-iteration to another. The only mean I see from the 
interface is to call for only one Newton iteration each time, then change the 
maximum residual from a call to another and loop until the convergence 
criterium is not reached.

Best Regards,

Yves

----- Mail original -----
De: "Moritz Jena" <address@hidden>
À: "getfem-users" <address@hidden>
Envoyé: Mardi 7 Mai 2019 16:23:00
Objet: [Getfem-users] Maximum allowed residuum

Dear GetFEM-Users,

I have written a FEM program, with which you can calculate technical 
springs numerically. 
Therefore I'm using the GetFEM-MATLAB-Interface 4.3 

These calculations are highly non-linear due to self-contact issues and 
large deformations.
That is the reason why technical springs have to be solved iteratively in 
several substeps.

The calculation by itself works very well. But I think I have a problem 
with the maximum allowed residuum that is passed to the solve command of 
getfem.
My theory is that the maximum allowed residuum has to be variable during 
the different substeps. 
By investigating these question online I found a paper of an university in 
Germany that contains the following for a equation system of 
A*x=b : ||delta_x||/||x|| <= Cond(A) * ||delta_b||/||b||
Unfortunatley these expression is not leading to plausible results. 

I'm also familiar using ansys. By using this commercial software I know 
that the maximum allowed residuum is changing by each iteration and by 
each substep.

All of the delivered getfem examples are using a constant maximum allowed 
residuum, no matter of high deformation or not.

So my question is, how am I able to find the maximum allowed residuum and 
by what expression? And do I have to define a variable maximum allowed 
residuum during the substeps to get reliable results out of the solve 
command?
 
Best regards,

Moritz Jena