ANA
ANA
CSPLINE( [ xtab, ytab] [, xnew][, d1, d2] [, /KEEP ,/SECOND, /GETDERIVATIVE])
Interpolates (using cubic splines) in the table of ytab
versus xtab (must be in ascending order with no duplicates)
at positions xnew. d1 and d2 are
(optional) values that the user requires for the first (default) or
second (/SECOND) derivatives at either end of the interpolation
interval. If they are not specified, then the second derivatives at
either end are set to zero (i.e., the so-called natural cubic spline).
/KEEP signals retention of xtab, ytab,
and the derived second derivatives for use in subsequent interpolations
from the same table. By default, the interpolated value at the
indicated positions is returned, but if /GETDERIVATIVE is
specified, then the first derivative at the indicated positions is
returned instead.
CSPLINE(xtab, ytab [, d1, d2] [, /SECOND, /GETDERIVATIVE]) prepares internal tables for subsequent interpolations
with CSPLINE(xnew [, /GETDERIVATIVE]). The internal table
is retained as if /KEEP had been specified.
CSPLINE(xnew [, /GETDERIVATIVE]) interpolates at positions
xnew in the retained table, and generates an error if no
table is yet available. If /GETDERIVATIVE is specified here but
was not specified when the table was installed, then the extra
auxilliary information is calculated on the fly rather than looked up in
the table: evaluation of the derivative is therefore fastest if
/GETDERIVATIVE is specified when the table is installed.
CSPLINE() clears the internal table that was retained. (In case
the table is real big and you want to get rid of it.)
See also: CSPLINE_EXTR, POLATE, TABLE, TENSE, TENSE_CURVE, TENSE_LOOP
[3.0.235]