[petsc-users] When to perform PETSc.Vec assembly with petsc4py

[SCOTTO Alexandre]

Hello Jose,

Thanks for your answer. Then it seems that I have under the hood usages of setValues() in my code since I do not explicitly make use of it but still has problems when not assembling my vector. Do I need to assemble vectors after Mat.mult or Scatter.scatter?

By the way, I did not know that PETSc.Vec objects supported direct assignments like x[i] = ..., so I rather use assignments of the form x.array = ...

>From what I understand from the GitHub page (https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/blob/main/src/binding/petsc4py/src/petsc4py/PETSc/Vec.pyx__;!!G_uCfscf7eWS!f3M5SmfhSqew4tgfvFDjdLnd3q3kT_KzcCitJTJC0HRl1YvbSNBr5Uuzv6OWP1pVQBgbi_WJlekerylpGcBHQ9vsbzL1suFBQHkoPIwhdw$ ) it seems, that doing so, we only access the local portion of the array which should not require any assemble() am I right?

Best regards,
Alexandre.


-----Message d'origine-----
De : Jose E. Roman <jroman at dsic.upv.es> 
Envoyé : mardi 15 juillet 2025 12:21
À : SCOTTO Alexandre <alexandre.scotto at irt-saintexupery.com>
Cc : petsc-users at mcs.anl.gov
Objet : Re: [petsc-users] When to perform PETSc.Vec assembly with petsc4py

Assembly is needed after a call to x.setValues() or any of its variants.
https://urldefense.us/v3/__https://petsc.org/main/petsc4py/reference/petsc4py.PETSc.Vec.html*petsc4py.PETSc.Vec.setValue__;Iw!!G_uCfscf7eWS!f3M5SmfhSqew4tgfvFDjdLnd3q3kT_KzcCitJTJC0HRl1YvbSNBr5Uuzv6OWP1pVQBgbi_WJlekerylpGcBHQ9vsbzL1suFBQHlKEPOyQg$ 
Take into account that in python the notation x[i] = ...  with call x.setValues() under the hood.

Jose


> El 15 jul 2025, a las 12:02, SCOTTO Alexandre via petsc-users <petsc-users at mcs.anl.gov> escribió:
> 
> Dear PETSc community,
>  As a beginner in the MPI world and with the PETSc library, I come with a possibly very naive question.
> I know from the documentation that assembling vectors must be done, but it is not clear to me when to perform this operation.
> Is there a simple way to know when a vector need be assembled and when it is not?
>  Thanks in advance.
> Regards,
> Alexandre.