# area2

Name:
`area2 - Return array of indices defining a 2d subarea of a 2d array.`
Synopsis:
```   source_anchor_y source_anchor_x    area_height   area_width   area_anchor_y   area_anchor_x    area2 -> [2d-indices]
```
Examples:
```   (Examples are illustrated):       Ex. 1: source array: (height=5), (width=10), anchor=(0,0)    subarea	 :  height=3,   width= 3,  anchor=(0,0)    xoo.......    ooo.......    ooo.......    ..........    ..........       0 0  3 3 0 0 area2 -> [0 0  0 1  0 2    1 0  1 1  1 2    2 0  2 1  2 2]       Ex. 1b:source array: (height=5), (width=10), anchor=(2,2)    subarea	 :  height=3,   width= 3,  anchor=(2,2)    ooo.......    ooo.......    oox.......    ..........    ..........       2 2  3 3 2 2 area2 -> [0 0  0 1  0 2    1 0  1 1  1 2    2 0  2 1  2 2]       Ex. 1c:Note that anchor point may lie outside both    arrays' bounds:    source array: (height=5), (width=10), anchor=(1,12)    subarea	 :  height=3,   width= 3,  anchor=(1,12)    ooo.......    ooo.......  x    ooo.......    ..........    ..........       1 12  3 3 1 12 area2 -> [0 0  0 1  0 2    1 0  1 1  1 2    2 0  2 1  2 2]       Ex. 2: source array: (height=6), (width=15), anchor=(2,5)    subarea	 :  height=4,   width= 5,  anchor=(1,3)    ...............    ..ooooo........    ..oooxo........    ..ooooo........    ..ooooo........    ...............       2 5  4 5 1 3 area2 -> [1 2  1 3  1 4  1 5  1 6    2 2  2 3  2 4  2 5  2 6    3 2  3 3  3 4  3 5  3 6    4 2  4 3  4 4  4 5  4 6]       Ex. 3: Note that subarea doesn't need to lie    inside bounds of source array:    source array: (height=4), (width= 8), anchor=(4,-1)    subarea	 :  height=2,   width= 3,  anchor=(1, 0)    ........    ........    ........    ooo......    xoo          4 -1  2 3 1 0 area2 -> [3 -1  3 0  3 1    4 -1  4 0  4 1]
```
Description:
```   Given a -- hypothetical -- twodimensional array,    "area" tells you, what indices you need to    subscript a contiguous, twodimensional subarea.       The subarea is defined by specifying it's size    (width and height), as well as its location in the    source array. The location is defined by specifying    an anchor point in the source array as well as in    the subarea. Anchor points are matched, see    illustration, and examples below:       source array: height=6, width=15, anchor=(2,5)    subarea	 : height=4, width= 5, anchor=(1,3)    ...............    ..ooooo........    ..oooxo........    ..ooooo........    ..ooooo........    ...............          "area2" returns an array of TWODIMENSIONAL indices.    There is a SLI function called "area" returning    onedimensional indices, as well as the conversion    functions "cv1d" and "cv2d".    (For information on the order of subscription in NEST    arrays, see references below.)
```
Parameters:
```   In: "area2" takes six integer arguments (three pairs).    These arguments describe (1) the height and width of the    subarea to be indexed in the (hypothetical) source array, as    well as (2&3) an anchor point in each of the two arrays (see    illustration above):       source_anchor_y,    source_anchor_x: position of the anchor point relative    to ORIGIN OF THE SOURCE ARRAY       area_heigh  t  : height of the subarea to be subscribed    area_width	 : width  of the subarea to be subscribed    area_anchor_y,    area_anchor_x  : position of the anchor point relative    to ORIGIN OF THE SUBAREA       Out: "area" returns an array of ONEDIMENSIONAL indices:       [2d-indices]   : flat integer array containing the indices    that can be used to subscript the    (hypothetical) source array in order to    access the desired subarea.       Indices are twodimensional. The returned    array is flat and has the following order:    [1y 1x  2y 2x  3y 3x  ...  ny nx]    That is, each pair of numbers indicates the    y- and the x-component of a respective    index.       The indices 1..n are returned in standard    NEST counting order. (For information on the    order of subscription in NEST arrays, see    references below.)
```
Diagnostics:
```   "area2" may raise the following SLI interpreter errors:    StackUnderflowError    ArgumentTypeError       No argument range check is performed. The returned    indices may indicate regions outside the source    array (see Example 3). This is not a bug, it's a    feature :-). Note that restrictions apply to the    related function "area".       However, anchor points may lie outside the array    bounds.       Note that arguments source_width and source_height are not used in    computation, and do not appear in the argument list.
```
References:
```(TO BE DONE: NEST layer indexing conventions)
```
Author:
```Ruediger Kupper
```
SeeAlso: Source:
`/home/graber/work-nest/nest-git/nest-simulator/sli/sliarray.cc`