[petsc-dev] Inquiry about a change in petsc version 3.19.1

[Barry Smith]

  Looks like a fatally flawed change I should never have made. I have an MR to revert it https://gitlab.com/petsc/petsc/-/merge_requests/6620 Should get into release and main by tommorow.

  Barry


> On Jun 19, 2023, at 4:37 PM, Barry Smith <bsmith at petsc.dev> wrote:
> 
> 
>   Sorry about this, we'll take a look and get back to you.
> 
> 
> 
>> On Jun 19, 2023, at 4:05 PM, Nabil Abboud via petsc-dev <petsc-dev at mcs.anl.gov> wrote:
>> 
>> Dear all,
>> 
>> We were trying to update the petsc version we use in our code to the version 3.19.1 when we noticed that some of the unit tests in our code started failing. The reason for the failure seems to be due to a change in the linesearch logic of petsc version 3.19.1. In particular, the implementation of the function SNESLineSearchGetTolerances was modified such that maxstep is now scaled with fnorm as shown in the following link https://gitlab.com/petsc/petsc/-/blob/main/src/snes/linesearch/interface/linesearch.c#L1097
>> This change seems to be inconsistent with the way maxstep is being used later on to compute a step size using the l2 line search algorithm, for instance, check the following code https://gitlab.com/petsc/petsc/-/blob/main/src/snes/linesearch/impls/l2/linesearchl2.c#L119 where maxstep is compared to lambda_update and where maxstep is scaled by fnorm whereas lambda_update seems to be a scalar of a different order as computed here https://gitlab.com/petsc/petsc/-/blob/main/src/snes/linesearch/impls/l2/linesearchl2.c#L111 .
>> The way this change is reflected in our code is that we were trying to enforce a range for the step size provided by the l2 line search between 0.1 and 1 and now with the new changes in petsc version 3.19.1 the upper limit seems not to hold anymore and we are seeing step sizes larger than 1.
>> 
>> Thank you in advance for your help.
>> Best regards,
>> Nabil
> 

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