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SUBROUTINE SHPLOK(X,Y,FX,FY,F,PPHI,W,R,N,DMUE,RR,PHI)
C********************************************************************
C *
C Program name: SHPLOK *
C *
C********************************************************************
C *
C This subroutine computes one functional value at (X,Y) for given*
C nodes using the local Shepard method. *
C *
C********************************************************************
C *
C *
C Input parameters: *
C ================= *
C X : X value for which we want to interpolate the Z value *
C Y : Y value for which we want to interpolate the Z value *
C FX, FY, F : vectors ..(0:N) with X and Y coordinates of nodes*
C (FX,FY) and corresponding functional value F. *
C N : Index of last node *
C DMUE : Exponent, 0 < DMUE < infinity, reasonable results can *
C be achieved for 2 < DMUE < 6. If on input DMUE <= 0, we *
C set DMUE = 2 internally. *
C RR : Radius around (X,Y) inside which all nodes are used to *
C interpolate at (X,Y). *
C *
C *
C AUX VECTORS: *
C ============ *
C W, R, PPHI : vectors ..(0:N) *
C *
C *
C Output parameters: *
C ================== *
C PHI : Interpolated Z value at (X,Y) *
C *
C *
C********************************************************************
C *
C Required subroutines: none *
C *
C********************************************************************
C *
C Author : Bjoern Terwege *
C Date : 6.12.1995 *
C Source code : FORTRAN 77 *
C *
C********************************************************************
IMPLICIT DOUBLE PRECISION (A-H,O-Z)
DIMENSION R(0:N),W(0:N),FX(0:N),FY(0:N),F(0:N),PPHI(0:N)
IF(DMUE.LT.0.) DMUE=2.
DO 20 I=0,N
R(I)=DSQRT(((X-FX(I))*(X-FX(I)))+
F ((Y-FY(I))*(Y-FY(I))))
IF (R(I).EQ.0) THEN
PHI=F(I)
GOTO 111
ENDIF
20 CONTINUE
C
C Compute the PPHI(I)
C
DO 40 I=0,N
IF(R(I).GE.RR) THEN
PPHI(I)=0
ELSE
PPHI(I)=(RR/R(I))-1
ENDIF
40 CONTINUE
C
C Compute the denominators of the weights
C
SUM=0
DO 50 J=0,N
IF(PPHI(J).EQ.0) GOTO 50
SUM = SUM+1/(PPHI(J)**DMUE)
50 CONTINUE
C
C Compute the weights
C
DO 60 J=0,N
IF(PPHI(J).EQ.0) THEN
W(J)=0
GOTO 60
ELSE
W(J)=1/(PPHI(J)**DMUE)*1/SUM
ENDIF
60 CONTINUE
C
C Compute the approximate function value Z at (X,Y)
C
PHI=0
DO 70 I=0,N
PHI=PHI+W(I)*F(I)
70 CONTINUE
111 CONTINUE
RETURN
END
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