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Interpolation/

spl_fstdrv.pro

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-elements (at least 2) input vector that specifies the tabulate points in ascending order.

y        in required

f(x) = y. An n-elements 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 type: scalar or array

The input values for which the first derivative values are desired.

Examples


   IDL> y2 =  spl_fstdrv(x, y, yscd, x2)

    

Version history

Version

$Id: spl_fstdrv.pro 372 2008-08-08 12:31:53Z pinsard $

History

Sebastien Masson (smasson@lodyc.jussieu.fr): May 2005

 


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