Interpolation/
spl_fstdrv.pro
SPL_FSTDRV returns the values of the first derivative of
the interpolating function at the points X2i. It is a double
precision array.
Given the arrays X and Y, which tabulate a function (with the X[i]
AND Y[i] in ascending order), and given an input value X2, the
SPL_INCR function returns an interpolated value for the given values
of X2. The interpolation method is based on cubic spline, corrected
in a way that interpolated value are also in ascending order
spl_fstdrv
result = spl_fstdrv(x, y, yscd, x2)
Return value
y2: f'(x2) = y2.
Parameters
x
in
required
An n-element (at least 2) input vector that specifies the
tabulate points in ascending order.
y
in
required
f(x) = y. An n-element input vector that specifies the values
of the tabulated function F(Xi) corresponding to Xi.
yscd
in
required
The output from SPL_INIT for the specified X and Y.
x2
in
required
The input values for which the first derivative values are desired.
X can be scalar or an array of values.
Examples
IDL> y2 = spl_fstdrv(x, y, yscd, x2)
Version history
Version
$Id: spl_fstdrv.pro 231 2007-03-19 17:15:51Z pinsard $
History
Sebastien Masson (smasson@lodyc.jussieu.fr): May 2005
Produced by IDLdoc 2.0.