[petsc-users] First shift renders no information

[Desforges Perceval]

Thank you very much, moving around the endpoints of the interval did
indeed solve my problem. 

Best regards,

---
Desforges Perceval 

Le 2018-09-17 17:51, Jose E. Roman a écrit :

> This can happen sometimes when the chosen interval for spectrum slicing is to large or the endpoints of the interval are too far away from the eigenvalues. Try moving the endpoints of the interval closer to the eigenvalues.
> 
> Jose
> 
>> El 17 sept 2018, a las 17:24, Desforges Perceval <perceval.desforges at ens-lyon.fr> escribió:
>> 
>> Hello PETSc developpers,
>> 
>> I have been using SLEPc and PETSc for solving my sparse systems for a small time now, and have been very satisfied with everything.
>> 
>> However, I have been running into an error lately, and I have been unable to find any online resource  that talks about this specific error.
>> 
>> I use SLEPc to find all the eigenvalues of certain tridiagonal and symmetric matrices. I set the solver to find all the eigenvalues in a large interval ([0;10] for example) using the spectrum splicing technique. I use MUMPS because I would like to perform this calculation in parallel later on, but for now I am doing it sequentially.
>> 
>> While the solver works very well for small enough matrices (n=2000), when I increase the matrix size to around 10000, I get this error that I do not really understand:
>> 
>> [0]PETSC ERROR: First shift renders no information
>> 
>> Could someone please enlighten me as to what this error means? I don't know if it's relevant but I am using older version of PETSc (3.8.4) and SLEPc (3.8.2).
>> 
>> I apologize in advance if this question has been answered somewhere already.
>> 
>> Thank you very much,
>> 
>> Sincerely,
>> 
>> Desforges Perceval
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