Peano's block-structured output format {#chapter:blockstructured-output-format}

Peano has introduced its own block-structured output format. Its idea is that a mesh is dumped as an unstructured set of cell where each cell is uniquely identified through its offset and its size. The mesh data format lacks any topological information (connectivity). A cell always is a patch, i.e. holds a (topological) Cartesian mesh of dimensions $k \times k$ or $k \times k \times k$, respectively. If you work without patches, $k=2$. In this case, the block format obviously can yield a significant overhead.

A minimal ASCII example file

# # Peano output file # Version 0.1 # format ascii dimensions 3 patch-size 6 6 6

begin vertex-metadata "identifier A" number-of-unknowns 58 meta-data "This is some fancy meta data" end vertex-values

begin vertex-metadata "time" number-of-unknowns 1 meta-data "This is some fancy meta data" end vertex-values

begin patch offset 0.0 0.0 0.0 size 0.5 0.5 0.5 begin vertex-values "identifier A" 18.0 123.0 ... end vertex-values begin vertex-values "time" 1.0 1.0 ... end vertex-values end patch

begin patch offset 0.5 0.0 0.0 size 0.25 0.25 0.25 ... end patch

This spec file specifies a simple grid that

The actual grid plotted consists of two patches (boxes discretised with a small regular grid).
Both small grids consist of $6 \times 6 \times 6$ cells. They all have the same size, i.e. are equally spaced.
Each vertex holds two sets of unknowns. The first set is called identifier A and each entry (per vertex) comprises 58 double unknowns. The second set of unknowns per vertex is called time and is a scalar quantity.
The data per cube is ordered lexicographically, i.e. we run along the x-axis first, then along the y-axis, and finally along the z-axis.
All data is held as SoA, i.e. we first give all the 58 unknowns of the first vertex within the cube, then the 58 unknowns of the right neighbour vertex, and so forth.
All output data is ASCII.
Patches may overlap in both space and time.

More sophiciated dumps

The file format supports cell-values.
Each vertex-values or cell-values section in the header of the file, i.e. not embedded into a patch, may have a section

begin mapping 0.0 0.0 0.0 0.1 0.1 0.1 0.4 0.4 0.4 ... end mapping

If no mapping is present, our code dumps a regular subgrid (patch) per patch region. If a mapping is present, the mapping has exactly $(6+1) \cdot (6+1) \cdot (6+1)$ entries in the example from the previous section. Each entry is a 3d coordinate relative to the unit cube and specifies how the topologially regular grid prescribed within a patch is to be mapped. You might for example plot points of the topologically regular grid with Gauß-Legendre spacing.
The plotter by default always creates two types of files: The actual data files as described above and one meta file. The meta file solely links to the actual data:

# # Peano patch file # Version 0.1 # format ASCII begin dataset include "conserved-1-rank-0.peano-patch-file" end dataset begin dataset include "conserved-2-rank-0.peano-patch-file" end dataset

Per snapshot (typically time step), the plotter adds on dataset entry. Each data set holds one data file per active rank. Each rank writes its actual data into a separate file.