# cellFaces

Find faces attached to specified cells

## Syntax

``FaceID = cellFaces(g,RegionID)``
``FaceID = cellFaces(g,RegionID,FilterType)``

## Description

example

````FaceID = cellFaces(g,RegionID)` finds faces attached to the cells with ID numbers listed in `RegionID`.```

example

````FaceID = cellFaces(g,RegionID,FilterType)` returns internal, external, or all faces attached to the cells with ID numbers listed in `RegionID`.```

## Examples

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Find faces attached to two cuboids in a geometry consisting of four stacked cuboids.

Create a geometry that consists of four stacked cuboids.

`gm = multicuboid(5,10,[1 2 3 4],'ZOffset',[0 1 3 6])`
```gm = DiscreteGeometry with properties: NumCells: 4 NumFaces: 21 NumEdges: 36 NumVertices: 20 Vertices: [20x3 double] ```

Plot the geometry with the cell labels.

`pdegplot(gm,'CellLabels','on','FaceAlpha',0.2)` Find faces attached to cells 1 and 3.

`faceIDs = cellFaces(gm,[1 3])`
```faceIDs = 1×12 1 2 3 4 5 6 7 12 13 14 15 16 ```

Plot the geometry with the face labels.

`pdegplot(gm,'FaceLabels','on','FaceAlpha',0.2)` Find faces attached to the outer cuboid in a geometry consisting of two nested cuboids.

Create a geometry that consists of two nested cuboids of the same height.

`gm = multicuboid([2 5],[4 10],3)`
```gm = DiscreteGeometry with properties: NumCells: 2 NumFaces: 12 NumEdges: 24 NumVertices: 16 Vertices: [16x3 double] ```

Plot the geometry with the cell labels.

`pdegplot(gm,'CellLabels','on','FaceAlpha',0.2)` Find all faces attached to the outer cell.

`faceIDs = cellFaces(gm,2)`
```faceIDs = 1×10 3 4 5 6 7 8 9 10 11 12 ```

Find only the internal faces attached to the outer cell. Internal faces are faces shared between multiple cells.

`faceIDs_int = cellFaces(gm,2,'internal')`
```faceIDs_int = 1×4 3 4 5 6 ```

Find only the external faces attached to the outer cell.

`faceIDs_ext = cellFaces(gm,2,'external')`
```faceIDs_ext = 1×6 7 8 9 10 11 12 ```

Plot the geometry with the face labels.

`pdegplot(gm,'FaceLabels','on','FaceAlpha',0.2)` ## Input Arguments

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3-D geometry, specified as a `DiscreteGeometry` object.

Cell ID, specified as a positive number or a vector of positive numbers. Each number represents a cell ID.

Type of faces to return, specified as `'internal'`, `'external'`, or `'all'`. Depending on this argument, `cellFaces` returns these types of faces:

• `'internal'` — Internal faces, that is, faces shared between multiple cells.

• `'external'` — External faces, that is, faces not shared between multiple cells.

• `'all'` — All faces attached to the specified cells.

## Output Arguments

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IDs of faces attached to the specified cells, returned as a positive number or a vector of positive numbers.

## Version History

Introduced in R2021a