PETSc hashing is done by leveraging the great package khash. Take a look at
include/petsc/private/hashtable.h and hashijkey.h for how we use kash to
automatically generate the code for a particular key. Just make your tolerance
smaller than the smallest diameters of your cells.
Barry
> On Nov 8, 2023, at 2:47 PM, Jed Brown <j...@jedbrown.org> wrote:
>
> I don't think you want to hash floating point values, but I've had a number
> of reasons to want spatial hashing for near-neighbor queries in PETSc and
> that would be a great contribution. (Spatial hashes have a length scale and
> compute integer bins.)
>
> Brandon Denton via petsc-users <petsc-users@mcs.anl.gov> writes:
>
>> 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?
>>
>> Thank you in advance for your time.
>> Brandon Denton
