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# Notations and conventions

This DPM uses a small, consistent set of notational conventions. Tensor shapes
are written as tuples in NumPy/PyTorch order, e.g. a tile is `(C, 256, 256)`
(channels, height, width) and an embedding matrix is `(N, 1024)` (number of
tiles, embedding dimension `D`). `C` denotes the band count of the source
modality (Sentinel-1 / Sentinel-2), `N` the number of embedded tiles and `D`
the embedding dimension. Symbol names and API identifiers (`encode`,
`tile_image`, `load_embeddings`, `stack_vectors`) are written verbatim in
`monospace` and match the corresponding Python names in the
[Software Design Document](../sdd/index), whose design standards govern naming
and coding conventions. Block-diagram symbol conventions are summarised below.

## Block diagram symbols

Block diagrams can be created using
[Mermaid flowcharts](https://mermaid.js.org/syntax/flowchart.html).

The following conventions apply:

A plain node illustrates an algorithm step:

```{mermaid}
flowchart
  step[Algorithm/Processing step]
```

A node in a subroutine shape illustrates an
algorithm step for which a further breakdown exists:

```{mermaid}
flowchart
  step[[Function]]
```

A node in a parallelogram shape illustrates data, e.g. internal data:
```{mermaid}
flowchart
  data[/Data/]
```

A node in a cylindrical shape illustrates external data, e.g. a database:
```{mermaid}
flowchart
  externalData[(Database)]
```

A node (rhombus) illustrates a decision step:
```{mermaid}
flowchart
  decision{Decision step}
```

A node with in a trapezoid shape illustrates the start of a loop:
```{mermaid}
flowchart
  start[/Start\]
```

A node with in an alternative trapezoid shape illustrates the end of a loop:
```{mermaid}
flowchart
  e[\End/]
```

Arrows in block diagrams indicate precedence: data input/output
to a step or logical succession of steps:
```{mermaid}
flowchart LR
  a[Step A]
  b[Step B]
  a --> b
```

Example diagram:
```{mermaid}
flowchart TD
  packet[/Packets/]
  annot[/Annotations/]
  a[Step A]
  b[Step B]
  packet --> a
  annot --> a
  a --> b
```