1 #pragma once 2 3 /* MANSEC = Vec */ 4 /* SUBMANSEC = PetscSection */ 5 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. 9 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. 12 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. 16 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. 20 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()` 25 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. 30 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. 34 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). 37 38 Level: beginner 39 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; 44 45 /*S 46 PetscSectionSym - Symmetries of the data referenced by a `PetscSection`. 47 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. 52 53 Level: developer 54 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; 59 60 /*J 61 PetscSectionSymType - String with the name of a `PetscSectionSym` type. 62 63 Level: developer 64 65 Note: 66 `PetscSectionSym` has no default implementation, but is used by `DM` in `PetscSectionSymCreateLabel()`. 67 68 .seealso: [PetscSection](ch_petscsection), `PetscSectionSymSetType()`, `PetscSectionSymGetType()`, `PetscSectionSym`, `PetscSectionSymCreate()`, `PetscSectionSymRegister()` 69 J*/ 70 typedef const char *PetscSectionSymType; 71