[petsc-users] Question about ordering of the gradient in DS

[Matthew Knepley]

On Mon, Dec 9, 2024 at 6:34 AM Gong Yujie <yc17470 at connect.um.edu.mo> wrote:

> Dear PETSc group,
>
> I would like to inquire about the storage of the gradient in function
> PetscDSSetResidual:
>
> PetscErrorCode PetscDSSetResidual(PetscDS ds, PetscInt f, void
> (*f0)(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[],
> const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[],
> const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[],
> const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[],
> PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar
> constants[], PetscScalar f0[]), void (*f1)(PetscInt, PetscInt, PetscInt,
> const PetscInt[], const PetscInt[], const PetscScalar[], const
> PetscScalar[], const PetscScalar[], const PetscInt[], const PetscInt[],
> const PetscScalar[], const PetscScalar[], const PetscScalar[], PetscReal,
> const PetscReal[], PetscInt, const PetscScalar[], PetscScalar[]))
>
> Assume u = (u1, u2, u3)^T, the gradient of u is
>
> In PetscDSSetResidual, it is stored in an array. Is it ordered as
> (u1x,u2x, u3x, u1y, u2y, u3y, u1z, u2z,u3z)?
>

It is a C array grad[Nc][dE], so that the spatial dimension is fastest

  ux, uy, ux, vx, vy, vz, wx, wy, wz

  Thanks,

     Matt


> Thanks in advance!
>
> Best Regards,
> Yujie
>


-- 
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

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