[VARIANT] = `SPARSE'

A sparse $<$ARRAY$>$ structure is used for storing the values of an array where most of the pixels are equal in value (zero perhaps). The structure is composed of a list of array indices for the specified ``non-grey'' elements, and their corresponding data values. The ``grey'' value adopted for the majority of the array elements is also supplied.

Table: Components of $<$ARRAY$>$ Structure, [VARIANT] = `SPARSE'

Component Name	TYPE	Brief Description
[VARIANT]	$<$_CHAR$>$	`SPARSE'
[ORIGIN(NAXIS)]	$<$integer$>$	origin of the data array
[DATA(NDATA)]	$<$numeric$>$	data values for pixel subset
[LIST(NAXIS,NDATA)]	$<$integer$>$	list of pixel array indices
[DIMENSIONS(NAXIS)]	$<$integer$>$	dimension of equivalent $<$numeric$>$ array
[GREY]	$<$numeric$>$	grey value

NAXIS

The number of axes in the array being represented.

[ORIGIN]

The pixel origin in each dimension. If this object is not present, each origin is assumed to be 1.

NDATA

This is the number of non-grey array elements.

[DATA]

These are the data values for significant array elements. Mandatory.

[LIST]

These are the array indices for each significant array value. Mandatory.

[DIMENSIONS]

This array contains the axis dimensions of the full data array. It is used to generate the equivalent $<$narray$>$. Mandatory.

[GREY]

This is the value used to fill the array elements not referenced in the [LIST] component. It should have the same primitive TYPE as [DATA]. If absent, it is assumed to be the bad-pixel magic value (for [DATA]'s primitive type) since the pixel's value is undefined.

The equivalent primitive type is the TYPE of [DATA].