[petsc-users] Creating multiple Vecs with petsc4py

[Samar Khatiwala]

Thanks Matt and Jed for the quick replies! That answers my immediate questions.

Best,

Samar

> On Feb 12, 2022, at 1:33 PM, Jed Brown <jed at jedbrown.org> wrote:
> 
> VecDuplicateVecs isn't implemented in petsc4py, but it internally just loops over VecDuplicate so you can use
> 
> qs = [x.duplicate() for i in range(4)]
> 
> y.maxpy(alphas, qs)
> 
> 
> where the Python binding here handles qs being a Python array.
> 
> Samar Khatiwala <samar.khatiwala at earth.ox.ac.uk> writes:
> 
>> Hello,
>> 
>> I’d like to create an array of Vecs in petsc4py by calling VecDuplicateVecs but I can’t find the corresponding method (I’ve tried various iterations such as q = x.duplicateVecs(4), etc). 
>> Is this not implemented in petsc4py? One workaround I’ve come up with is something like:
>> 
>> q={}
>> for i in range(0, 3):
>>    q[i]=x.duplicate()
>> 
>> Is there another/better way? And how do I then use PETSc functions that operate on Vecs (e.g., VecMAXPY)? Would I just call VecAXPY in a loop as above?
>> 
>> Ultimately, what I really want to do is wrap my own C functions with Cython that take an array of Vecs as an argument and then operate on them. (The function needs the entire array 
>> of Vecs to do its thing so I can’t loop over the elements of the array.) For instance, I want to pass the q above to myCfunc(Vec *q, Vec *qout). How do I go about doing that?
>> 
>> Thanks very much!
>> 
>> Best,
>> 
>> Samar