1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
|
subroutine tuispl (xa, ya, y2, x, y)
C
C Interpolate at point X using cubic splines. The array Y2 must have
C previously been computed by calling TUCSPL. Note that XA, YA, Y2
C are two-element subarrays of the arrays with the same names elsewhere.
C Input and output are all double precision.
C This routine was copied with slight modifications from the SPLINT
C subroutine in Numerical Recipes by Press, Flannery, Teukolsky and
C Vetterling.
C
C XA i: pair of independent-variable values
C YA i: pair of dependent-variable values
C Y2 i: second derivatives of YA at each point
C X i: value at which spline is to be computed
C Y o: interpolated value at X
C
CH Phil Hodge, 14-Apr-1988 Subroutine copied from Numerical Recipes SPLINT.
C
double precision xa(2), ya(2), y2(2), x, y
C--
double precision h, a, b
h = xa(2) - xa(1)
a = (xa(2) - x) / h
b = (x - xa(1)) / h
y = a * ya(1) + b * ya(2) +
+ ((a**3 - a) * y2(1) + (b**3 - b) * y2(2))
+ * h * h / 6.
return
end
|
