V3FIT
seval2.f
1 C******************** START FILE SEVAL2.FOR ; GROUP TRKRLIB ************
2 C
3  REAL FUNCTION SEVAL2(N, U, X, Y, B, C, D, deriv)
4  INTEGER N
5  REAL U, X(N), Y(N), B(N), C(N), D(N), deriv
6 C
7 CCCCCCCCCCCCCCC
8 CCCCCCCCCCCCCCC
9 C THIS SUBROUTINE EVALUATES THE CUBIC SPLINE FUNCTION
10 C
11 C SEVAL2 = Y(I) + B(I)*(U-X(I)) + C(I)*(U-X(I))**2 + D(I)*(U-X(I))**3
12 C
13 C and the derivative
14 C
15 C deriv = B(i) + 2*C(i)*(U-X(i)) + 3*D(i)*(U-X(i))**2
16 C
17 C WHERE X(I) .LT. U .LT. X(I+1), USING HORNER'S RULE
18 C
19 C IF U .LT. X(1) THEN I = 1 IS USED.
20 C IF U .GE. X(N) THEN I = N IS USED.
21 C
22 C INPUT..
23 C
24 C N = THE NUMBER OF DATA POINTS
25 C U = THE ABSCISSA AT WHICH THE SPLINE IS TO BE EVALUATED
26 C X,Y = THE ARRAYS OF DATA ABSCISSAS AND ORDINATES
27 C B,C,D = ARRAYS OF SPLINE COEFFICIENTS COMPUTED BY SPLINE
28 C
29 C IF U IS NOT IN THE SAME INTERVAL AS THE PREVIOUS CALL, THEN A
30 C BINARY SEARCH IS PERFORMED TO DETERMINE THE PROPER INTERVAL.
31 C
32  INTEGER I, J, K, ILIN
33  REAL DX
34  DATA i/1/
35  DATA ilin/0/
36 C
37  IF ( i .GE. n ) i = 1
38  IF ( u .LT. x(i) ) GO TO 10
39  IF ( u .LE. x(i+1) ) GO TO 30
40 C
41 C BINARY SEARCH
42 C
43  10 i = 1
44  j = n+1
45  20 k = (i+j)/2
46  IF ( u .LT. x(k) ) j = k
47  IF ( u .GE. x(k) ) i = k
48  IF ( j .GT. i+1 ) GO TO 20
49 C
50 C EVALUATE SPLINE
51 C
52  30 dx = u - x(i)
53  IF(ilin.EQ.0) THEN
54  seval2 = y(i) + dx*(b(i) + dx*(c(i) + dx*d(i)))
55  deriv = b(i) + dx*(2.0*c(i) + dx*3.0*d(i))
56  ELSE
57  IF(i.EQ.n) THEN
58  zslop=(y(n)-y(n-1))/(x(n)-x(n-1))
59  ELSE
60  zslop=(y(i+1)-y(i))/(x(i+1)-x(i))
61  ENDIF
62  seval2=y(i)+dx*zslop
63  deriv=zslop
64  ENDIF
65 C
66  RETURN
67  END
68 C******************** END FILE SEVAL2.FOR ; GROUP TRKRLIB **************
deriv
Definition: mapout_nc.f:94