1: #pragma once

  3: /* MANSEC = Vec */
  4: /* SUBMANSEC = PetscSection */

  6: /*S
  7:   PetscSection - Provides a mapping from integers in a designated domain (defined by bounds `startp` to `endp`) to integers which can then be used
  8:   for accessing entries in arrays, other `PetscSection`s, `IS`s, `Vec`s, and `Mat`s.

 10:   One can think of `PetscSection` as a library-based tool for indexing into multi-dimensional jagged arrays which is needed
 11:   since programming languages do not provide jagged array functionality baked into their syntax.

 13:   The domain, `startp` to `endp`, is called the chart of the `PetscSection()` and is set with `PetscSectionSetChart()` and accessed
 14:   `PetscSectionGetChart()`. `startp` does not need to  be 0, `endp` must be greater than or equal to `startp` and the bounds
 15:   may be positive or negative.

 17:   The range of a `PetscSection` is in the space of
 18:   contiguous sets of integers. These ranges are frequently interpreted as domains (charts, meaning lower and upper bounds) of other array-like objects,
 19:   especially other `PetscSection`s, `IS`s, and `Vec`s.

 21:   For each point in the chart (from `startp` to `endp`) of a `PetscSection`, the output set is represented through an `offset` and a
 22:   `count`, which can be obtained using `PetscSectionGetOffset()` and `PetscSectionGetDof()` respectively and can be set via
 23:   `PetscSectionSetOffset()` and `PetscSectionSetDof()`. Lookup is typically using
 24:   accessors or routines like `VecGetValuesSection()`

 26:   The indices returned by the `PetscSection`
 27:   are appropriate for the kind of `Vec` it is associated with. For example, if the vector being indexed is a local vector, we call the section a
 28:   local section. If the section indexes a global vector, we call it a global section. For parallel vectors, like global vectors, we use negative
 29:   indices to indicate dofs owned by other processes.

 31:   Typically `PetscSections` are first constructed via a series of calls to `PetscSectionSetOffset()` and `PetscSectionSetDof()`, finalized via
 32:   a call to `PetscSectionSetup()` and then used to index into arrays and other PETSc objects. The construction (setup) phase corresponds to providing all
 33:   the information needed to define the multi-dimensional jagged array structure.

 35:   `PetscSection` is used heavily by `DMPLEX`. Simplier `DM`, such as `DMDA`, generally do not need `PetscSection` since their array access patterns
 36:   are simplier and can be fully expressed using standard programming language array syntax, see [DM commonality](ch_dmcommonality).

 38:   Level: beginner

 40: .seealso: [PetscSection](ch_petscsection), `PetscSectionCreate()`, `PetscSectionGetOffset()`, `PetscSectionGetOffset()`, `PetscSectionSetChart()`,
 41:           `PetscSectionGetChart()`, `PetscSectionDestroy()`, `PetscSectionSym`, `PetscSectionSetup()`, `DM`, `DMDA`, `DMPLEX`
 42: S*/
 43: typedef struct _p_PetscSection *PetscSection;

 45: /*S
 46:   PetscSectionSym - Symmetries of the data referenced by a `PetscSection`.

 48:   Often the order of data index by a `PetscSection` is meaningful, and describes additional structure, such as points on a
 49:   line, grid, or lattice.  If the data is accessed from a different "orientation", then the image of the data under
 50:   access then undergoes a symmetry transformation.  A `PetscSectionSym` specifies these symmetries.  The types of
 51:   symmetries that can be specified are of the form R * P, where R is a diagonal matrix of scalars, and P is a permutation.

 53:   Level: developer

 55: .seealso: [PetscSection](ch_petscsection), `PetscSection`, `PetscSectionSymCreate()`, `PetscSectionSymDestroy()`, `PetscSectionSetSym()`, `PetscSectionGetSym()`, `PetscSectionSetFieldSym()`,
 56:           `PetscSectionGetFieldSym()`, `PetscSectionGetSymPoints()`, `PetscSectionSymType`, `PetscSectionSymSetType()`, `PetscSectionSymGetType()`
 57: S*/
 58: typedef struct _p_PetscSectionSym *PetscSectionSym;

 60: /*J
 61:   PetscSectionSymType - String with the name of a `PetscSectionSym` type.

 63:   Level: developer

 65:   Note:
 66:   `PetscSectionSym` has no default implementation, but is used by `DM` in `PetscSectionSymCreateLabel()`.

 68: .seealso: [PetscSection](ch_petscsection), `PetscSectionSymSetType()`, `PetscSectionSymGetType()`, `PetscSectionSym`, `PetscSectionSymCreate()`, `PetscSectionSymRegister()`
 69: J*/
 70: typedef const char *PetscSectionSymType;