HELP ARRAYSLICE                             David Young, August 1998


LIB * ARRAYSLICE provides procedures for accessing and updating an N-1
dimensional "slice" of an N dimensional array.

arrayslice(arrin, dim, i, arrout, regionout) -> arrout
        The first argument arrin is an array, of say N dimensions. A
        "slice" of this array is defined by those elements whose dim'th
        index is i. For example, for a 2-D image array whose first index
        refers to the column and whose second index refers to the row,
        dim = 1 means extract the i'th column, and dim = 2 means extract
        the i'th row. For a 3-D input array, a slice is a 2-D plane, and
        so on. dim and i must be integers.

        The result will have one fewer dimension than the input, and the
        condition satisfied on exit is thus

            arrin(<dim-1 indices>, i, <N-dim indices>)
            = arrout(<same dim-1 indices>, <same N-dim indices>)

        for all sets of indices that refer to points in the input and
        output regions as defined below.

        On entry, arrout may be an array which is to receive the data.
        In this case, the same array is returned as the result after
        some or all of its elements have been updated. Alternatively
        arrout may be <false> on entry, in which case a new array is
        created and returned.

        The region from which data are taken is defined as follows. If
        arrout and regionout are both <false>, then the whole of the
        slice of the input array is copied. For example, if the input
        array has boundslist [1 10 2 20 3 30] and dim = 2, then the
        newly created output array will have boundslist [1 10 3 30].

        if regionout is not <false> it must be a list of *boundslist
        type which specifies the region of the output array in which to
        store data. If a new array is created, then regionout will
        become its boundslist; otherwise parts of arrout outside
        regionout will not be changed. In either case, regionout also
        specifies the part of the input slice from which data are to be
        taken. For example, if regionout is [2 5 3 13], dim = 2 and i =
        10, then data will be taken from the region of the 3-D input
        array given by [2 5 10 10 3 13]. This region must be contained
        within arrin's array bounds.

        If arrin is an array and regionout is <false>, then the output
        region is taken to be the whole of arrin, whose boundslist must
        therefore not go outside the input slice bounds.

(arrin, regionin) -> arrayslice(arrout, dim, i)
        In the updating form, arrin has N-1 dimensions and arrout has N
        dimensions. Data from arrin are copied into the slice of arrout
        defined by dim and i as described above. The relationship
        between elements of arrin and arrout when the procedure returns
        is

            arrout(<dim-1 indices>, i, <N-dim indices>)
            = arrin(<same dim-1 indices>, <same N-dim indices>)

        If regionin is <false>, then the whole of arrin is copied to
        the slice, which must be large enough to contain it. Otherwise,
        regionin must be a *boundslist type list specifying the part of
        arrin from which data are taken.


--- $popvision/help/arrayslice
--- Copyright University of Sussex 1998. All rights reserved.