	(REGULAR VERB)

	Syntax:  MFILL(distance)

	MFILL takes the contents of Matrix (0), copies them to
	Matrix(1), and interpolates the matrix at any undefined
	values, placing the results into Matrix (0).

	MFILL takes a single argument which defines the radius, in
	units of grid cells, within which the interpolation will
	consider nearest-neighbor points. Radius must be greater than,
	or equal to, one pixel width.  For each undefined point, the
	algorithm searches along both the x- and y-axes, and the
	diagonals, through the point and finds the nearest neighbor
	pairs (if any) possessing valid data at distances of less than
	or equal to radius for each of these directions. An approximate
	value at the undefined point is computed via linear
	interpolation for any of the four directions having a valid
	data pair.  Then the weighted mean of the interpolated values
	is taken, with weights assigned proportional to the distances
	between the 'nearest neighbor pairs'.  If no valid 'adjacent
	pairs' are found, the undefined point is left undefined.

	While a large value of radius will fill in more holes, a
	smaller value gives greater assurance that the filled-in value
	bears a reasonable relation to reality. The interpolated values
	themselves are not used in filling in other undefined points.
	The area over which the operation is applied is defined by the
	adverbs MXMIN, MXMAX, MYMIN and MYMAX, but no values are filled
	in for the border cells of the matrix.

	ADVERBS USED:

	MXMIN, MXMAX    Limits in cell numbers along the x-axis
			for which Matrix (0) values will be processed.

	MYMIN, MYMAX    Limits in cell numbers along the y-axis
			for which Matrix (0) values will be processed.


	No adverbs are set by MFILL.

	If Matrix (1) contains something, you may want to MMOVE
	the matrix to somewhere else before using MFILL.

	EXAMPLE:

	Suppose that you have a few 'data holes' in Matrix (0) due to
	editing-out interference. Further, suppose that these holes lie
	within the region with bottom left-hand, and top right-hand,
	corners given by pixels (27,35), (93,117). If the largest holes
	occupy only two 'adjacent' undefined points, you can
	interpolate their values by typing,

		MXMIN = 27; MYMIN = 35; MXMAX = 93; MYMAX = 117
		MFILL(2)

