SOM Toolbox Online documentation http://www.cis.hut.fi/projects/somtoolbox/

vis_patch

Syntax

```  p = vis_patch(lattice)

```

Description

``` Forms a map unit patch for SOM_CPLANE function. Mainly a subroutine
of SOM_CPLANE, although can be used for on its own as well.

```

Required input arguments

``` lattice (string)

'hexa'  produces vertex coordiantes for a hexagoanl patch which
has its center on (0,0), unit width, and a height of
1.3334 units. This is not a regular hexagon but such that
the node which has topological coordinates (a,b) has its
center in the visualization at coordinates (a,b) for odd
a and at (a,b+.5) for even a. The non-regular look of the
patch is taken care simply by changing the axis ratio.

'rect'  produces vertex coordinates for a uniform rectangular patch.
having its center on (0,0) and unit sidelength. Used as a
subfunction in SOM_CPLANE.

'hexagon' produces vertex coordinates for a regular hexagonal patch.
It may be used in som_cplane if, for some reason, truly
regular hexagons are needed instead of the default unit
markers which are not uniform, but have integer
y-coordinates in the lattice.

```

Output arguments

``` p (matrix) The 2-dimensional vertex coordinates:

case 'rect'        case 'hexa'                case 'hexagon'
p=[[-.5 -.5];...     p=[[0     0.6667];...    p=[[0     0.5774];...
[-.5  .5];...        [0.5   0.3333];...       [0.5   0.2887];...
[ .5  .5];...        [0.5  -0.3333];...       [0.5  -0.2887];...
[ .5 -.5]];          [0    -0.6667];...       [0    -0.5774];...
[-0.5 -0.3333];...       [-0.5 -0.2887];...
[-0.5  0.3333]];         [-0.5  0.2887]];

```

Examples

```  som_cplane(vis_patch('rect'),[6 5],'none');
% this produces the same result as som_cplane('rect',[6 5], 'none')

som_cplane(vis_patch('hexa'), vis_unit_coord('hexa',[6 5]), 'none');
% produces in principle the same result as
% som_cplane(vis_patch('hexa'),[6 5],'none'),
% _but_ in this case the axis are not rescaled and the non-regular
% shape of hexagons can be seen.

som_cplane(vis_patch('hexagon'), som_unit_coords([6 5],'hexa'), 'none');
% produces a truly regular hexa lattice

```