[petsc-users] KSP number of iterations different from size of residual array

[Barry Smith]

  Sorry, sent the message too quickly. What I said below is incorrect.

  Barry


> On Jan 10, 2024, at 8:30 PM, Barry Smith <bsmith at petsc.dev> wrote:
> 
> 
>   Kevin,
> 
>     The manual page is misleading. It actually returns the total length of the history as set by KSPSetResidualHistory(), not the number of iterations.
> 
>   Barry
> 
> 
>> On Jan 10, 2024, at 7:09 PM, Kevin G. Wang <kevinw3 at vt.edu> wrote:
>> 
>> Hello everyone!
>> 
>> I am writing a code that uses PETSc/KSP to solve linear systems. I just realized that after running "KSPSolve(...)", the number of iterations given by 
>> 
>> KSPGetIterationNumber(ksp, &numIts)
>> 
>> is *different* from the size of the residual history given by
>> 
>> KSPGetResidualHistory(ksp, NULL, &nEntries);
>> 
>> That is, "numIts" is not equal to "nEntries". Is this expected, or a bug in my code? (I thought they should be the same...)
>> 
>> I have tried several pairs of solvers and preconditioners (e.g., fgmres & bjacobi, ibcgs & bjacobi). This issue happens to all of them.
>> 
>> Thanks!
>> Kevin
>> 
>> --
>> Kevin G. Wang, Ph.D.
>> Associate Professor
>> Kevin T. Crofton Department of Aerospace and Ocean Engineering
>> Virginia Tech
>> 1600 Innovation Dr., VTSS Rm 224H, Blacksburg, VA 24061
>> Office: (540) 231-7547  |  Mobile: (650) 862-2663 
>> URL: https://www.aoe.vt.edu/people/faculty/wang.html 
>> Codes: https://github.com/kevinwgy
> 

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