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spl1.f
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2002-06-11
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913b
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37 lines
C
C PAGE 261: NUMERICAL MATHEMATICS AND COMPUTING, CHENEY/KINCAID, 1985
C
C FILE: SPL1.FOR
C
C INTERPOLATES TABLE USING A FIRST-DEGREE SPLINE FUNCTION (SPL1)
C
DIMENSION T(10),Y(10),Z(10),C(10)
DATA (T(I),I=1,5)/1.,2.,3.,4.,5./
DATA (Y(I),I=1,5)/0.,1.,0.,1.,0./
C
N = 5
Z(1) = SPL1(N,T,Y,1.)
Z(2) = SPL1(N,T,Y,2.)
Z(3) = SPL1(N,T,Y,3.)
Z(4) = SPL1(N,T,Y,4.)
Z(5) = SPL1(N,T,Y,5.)
Z(6) = SPL1(N,T,Y,2.25)
Z(7) = SPL1(N,T,Y,4.5)
C
PRINT 5,Z
5 FORMAT(5X,10F10.5)
END
FUNCTION SPL1(N,T,Y,X)
DIMENSION T(N),Y(N)
DO 2 I = N-1,2,-1
DIFF = X - T(I)
IF(DIFF .GE. 0.0) GO TO 3
2 CONTINUE
I = 1
DIFF = X - T(1)
3 XM = (Y(I+1) - Y(I))/(T(I+1) - T(I))
SPL1 = Y(I) + XM*DIFF
RETURN
END