[petsc-users] non linear solver options

[Barry Smith]

   Does Newton’s method with SNESSetVariableBounds() fail to converge? Can you send the output of running with -ksp_monitor_true_residual -snes_monitor -snes_linesearch_monitor? 

    I’m guessing you are trying to impose the additional conditions because Newton’s method "gets stuck”? Or why else do you want those additional constraints?

   Barry

On Jan 18, 2014, at 2:52 PM, Dharmendar Reddy <dharmareddy84 at gmail.com> wrote:

> Hello,
>                 I am solving a set of equations with SNES
> F1 (x1,x2,x3) = 0
> F2 (x1,x2,x3) = 0
> F3 (x1,x2,x3) = 0
> 
> The system of equations is shown on page 1 of pdf here
> http://dunham.ee.washington.edu/ee531/notes/SemiRev.pdf
> 
> F1 = equation 1
> F2 = equation 2
> F3 = equation 5
> 
> x1 = n, X2=p and X3 = psi,
> X1 and X2 have an exponential dependance on X1
> after i scale the variables, X3 typically varies between say +/- 100
> where as X1 and X2 vary between 0 to 2. norm(X) then may usually
> dominated by solution values of X3.
> 
> Can you suggest me the snes options that i need to use to achieve the following:
> 
> 1. X1 > 0 and X2 > 0  (as per previous emails, i can use SNESSetVariableBounds)
> 2. I want the updates to solution to have an adaptive stepping based
> on norm of (F) or norm(X). If norm(F) is decreasing as the iteration
> progresss, larger stepping others wise reduce the step size..
> Similarly for Norm of X.
> 
> Can i get the work done with existing petsc routines/ options ?
> 
> Do i need to impliment the update method via SNESPOSTCheck  ?
> 
> 
> Thanks
> Reddy