[petsc-users] Storing Values using a Triplet for using later

[Matthew Knepley]

On Wed, Nov 8, 2023 at 2:40 PM Brandon Denton via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Good Afternoon,
>
> Is there a structure within PETSc that allows storage of a value using a
> triple similar to PetscHMapIJSet with the key using a struct{PetscScalar i,
> j, k;}?
>
> I'm trying to access mesh information (the shape function coefficients I
> will calculate prior to their use) who's values I want to store in the
> auxiliary array available in the Residual Functions of PETSc's FEM
> infrastructure. After some trial and error work, I've come to the
> realization that the coordinates (x[]) available in the auxiliary functions
> is the centroid of the cell/element currently being evaluated. This triplet
> is unique for each cell/element for a valid mesh so I think it's reasonable
> to use this triplet as a key for looking up stored values unique to each
> cell/element. My plan is to attached the map to the Application Context,
> also available to Auxiliary Functions, to enable these calculations.
>
> Does such a map infrastructure exist within PETSc? If so, could you point
> me to a reference for it? If not, does anyone have any suggestions on how
> to solve this problem?
>

As Jed says, this is a spatial hash. I have a primitive spatial hash now.
You can use DMLocatePoints() to find the cell containing a point (like the
centroid). Let me know if this does not work or if I misunderstand the
problem.

  Thanks!

    Matt


> Thank you in advance for your time.
> Brandon Denton
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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