#======================================================================

#                    . N M I N T E R P . L I N E A R 

#                    doc: Wed Nov 22 21:01:09 2000

#                    dlm: Fri Aug 30 13:26:58 2019

#                    (c) 2000 A.M. Thurnherr

#                    uE-Info: 101 9 NIL 0 0 72 0 2 4 NIL ofnI

#======================================================================

# linear interpolation for [fillgaps]

# HISTORY:

#	Apr  6, 2006: - created from [.interp.linear]

#	Jul 28, 2006: - added xf to ISInit() args

#	Jul 30, 2006: - added max-gap support

#	Aug  8, 2008: - documentation

#	Sep 23, 2011: - added support for %RECNO

#				  - removed xv from interp() args

#	Oct 19, 2011: - code did not work for %RECNO and trailing missing vals

#	Jan 23, 2014: - implemented huge speedup for sparse files

# NOTES:

#	- in contrast to the [.interp.*] routines, the [.nminterp.*] routines:

#		1) do not assume that x values increase monotonically

#		2) can handle nans

#		3) cannot be used with multiple buffers

#		4) use %RECNO when xfnr==-1

#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

#

# THE FOLLOWING VARIABLES MUST BE SET GLOBALLY (i.e. during loading)

#

#	$ISOpts				string of allowed options

#	$ISOptsUsage		usage information string for options

#

#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

$ISOpts = "";

$ISOptsUsage = "";

#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

#

# &ISUsage() 	mangle parameters (options, really)

#

#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

sub ISUsage() {}

#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

#

# &ISInit(f,xf)				init interpolation of field f

#       f					field number

#		xf					x field number or -1 for %RECNO

#       <ret val>           none

#

#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

sub ISInit($$) {}

#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

#

# &interpolate(xf,mg,f,lvr,cr)		interpolate field f

#		xf							x field or -1 for %RECNO

#		mg							max allowed x gap

#		f							field number to interpolate

#		lvr							last record with valid y val

#		cr							current record

#		<ret val>					interpolated value

#

# NB:

#	- handle f == xf

#	- return undef if interpolation cannot be carried out

#	- x VALUES MAY NOT BE MONOTONIC

#

#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

{ my(@nvr);		# static: next valid record (per field)

	sub interpolate($$$$$$)

	{

		my($xf,$mg,$f,$lvr,$cr) = @_;

		return $ants_[$cr][$xf] if ($xf == $f);

		return $ants_[$lvr][$f] 				# edge value is ok

			if ($xf>=0 && equal($ants_[$cr][$xf],$ants_[$lvr][$xf])) ||

			   ($xf<0 && $cr==$lvr);

		unless ($nvr[$f] > $cr) {

			$nvr[$f] = $cr + 1;

			while ($nvr[$f] <= $#ants_ && !numberp($ants_[$nvr[$f]][$f])) { $nvr[$f]++; }

		}

		return undef if ($nvr[$f] > $#ants_);

		return undef

			if ($xf>=0 && abs($ants_[$nvr[$f]][$xf]-$ants_[$lvr][$xf])>$mg);

		return $ants_[$nvr[$f]][$f] 				# edge value is ok

			if ($xf>=0 && equal($ants_[$cr][$xf],$ants_[$nvr[$f]][$xf])) ||

			   ($xf<0 && $cr==$nvr[$f]);

		if ($xf < 0) {

			die("$nvr[$f] - $lvr") unless ($nvr[$f] - $lvr > 0);

        }

		my($sc) = ($xf >= 0)

				? ($ants_[$cr][$xf] - $ants_[$lvr][$xf]) / ($ants_[$nvr[$f]][$xf] - $ants_[$lvr][$xf])

				: ($cr - $lvr) / ($nvr[$f] - $lvr);

		return $ants_[$lvr][$f] + $sc * ($ants_[$nvr[$f]][$f] - $ants_[$lvr][$f]);

	}

} # static scope

#----------------------------------------------------------------------

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