The
SPL_INIT
function is called to establish the type of interpolating
spline for a tabulated set of functional values *
X*
_{
i}
, *
Y*
_{
i}
= *
F*
(*
X*
_{
i}
). SPL_INIT returns the values of the 2nd derivative of the interpolating function at the points *
X*
_{
i}
.

It is important to realize that SPL_INIT should be called only *
once*
to process an entire tabulated function in arrays *
X*
and *
Y*
. Once this has been done, values of the interpolated function for any value of *
X*
can be obtained by calls (as many as desired) to the separate function SPL_INTERP.

SPL_INIT is based on the routine spline described in section 3.3 of *
Numerical Recipes in C: The Art of Scientific Computing*
(Second Edition), published by Cambridge University Press, and is used by permission.

X = (FINDGEN(21)/20.) * 2.0*!PI

PRINT, SPL_INIT(X, Y, YP0 = -1.1, YPN_1 = 0.0)

23.1552 -6.51599 1.06983 -1.26115 -0.839544 -1.04023

-0.950336 -0.817987 -0.592022 -0.311726 2.31192e-05 0.311634

0.592347 0.816783 0.954825 1.02348 0.902068 1.02781

PRINT, SPL_INIT(X, Y, YP0 = -1.1)

23.1552 -6.51599 1.06983 -1.26115 -0.839544 -1.04023

-0.950336 -0.817988 -0.592020 -0.311732 4.41521e-05 0.311555

SPL_INTERP , SPLINE , SPLINE_P