# Command: area2

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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:

- area

Source:

    /opt/conda/conda-bld/nest_1512418852064/work/nest-2.12.0/sli/sliarray.cc

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