[petsc-users] Regarding SNESSetFunction and SNESSetJacobian

[baikadi pranay]

Hello,
I have a couple of questions regarding how SNESSetFunction,SNESSetJacobian
and SNESSolve work together. I am trying to solve a nonlinear system of the
form A(x)x=b(x). I am using Fortran90. The way I intend to solve the above
equation is as follows:
Step 1: initialize x with an initial guess
Step 2: Solve using SNESSolve for (x^i, i is the iteration number,
i=1,2,3...)
Step 3: Calculate the update and check if it is less than tolerance
Step 4: If yes, end the loop. Else the jacobian matrix and function should
be updated using x^(i) and go back to step 2.

The part which is a little confusing to me is in understanding how to
update the jacobian matrix and the function F (= A(x)x-b(x)).

1) Should I explicitly call the subroutines Form Function and FormJacobian
by using x^i as the input argument or is this automatically taken care of
when I go back to step 2 and call SNESSolve?
2) If the answer to the above question is yes, I do not fully understand
the role played by the functions SNESSetFunction and SNESSetJacobian.

I apologize if I am not clear in my explanation. I would be glad to
elaborate on any section of my question. Please let me know if you need any
further information from my side.

Thank you,
Sincerely,
Pranay.
ᐧ
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20201009/e7878825/attachment.html>