LANCZOS

Appendix A Sec27.

LANCZOS

LANCZOS(A, F1, F2, N ) Returns the argument, bandpass-filtered in time using a Lanczos filter.

Arguments:	A	Variable with a regular time axis; may be a function of x, y, and/or z
	F1	Low frequency cutoff
	F2	High frequency cutoff
	N	Number of weights (must be odd)
Result Axes:	X	Inherited from A
	Y	Inherited from A
	Z	Inherited from A
	T	Inherited from A

For details see: Duchon, C. E., 1979: Lanczos filtering in one and two dimensions. J. of App. Met., 18, 1016-1022. This function is based on code written by Bill Gustafson at UC Davis.

Example: apply filter to series after removing its mean.

yes? use monthly_navy_winds
yes? let aa = uwnd[i=50,j=20]
yes? let az = aa - aa[t=@ave]
yes? plot az
yes? plot/over lanczos(az, 0.05, 0.1, 11)
yes? plot/over lanczos(az, 0.1, 0.2, 11)