# Example 1 - a simple 3D interpolation (Fortran double precision)

```      PROGRAM DSEX01
C
PARAMETER (NUM=1000, NX=21, NY=21, NZ=21)
C
C Define error file, Fortran unit number, and workstation type,
C and workstation ID.
C
PARAMETER (IERRF=6, LUNIT=2, IWTYPE=1, IWKID=1)
C
DOUBLE PRECISION XI(NUM), YI(NUM), ZI(NUM), U(NUM)
DOUBLE PRECISION XO(NX),  YO(NY),  ZO(NZ),  OUTPUT(NX,NY,NZ)
DOUBLE PRECISION XMIN,    YMIN,    ZMIN
DOUBLE PRECISION XMAX,    YMAX,    ZMAX
REAL             XP(NX),  YP(NY),  ZP(NZ),  OUTP(NX,NY,NZ)
INTEGER I, J, K, IER
C
DATA XMIN,YMIN,ZMIN/ -2.D0, -2.D0, -2.D0/
DATA XMAX,YMAX,ZMAX/  2.D0,  2.D0,  2.D0/
C
C  Create random data in three space and define a function.
C  To get this to work on your system, you may have to insert
C  the correct random number generator for your compiler.
C
DO 10 I=1,NUM
XI(I) = XMIN+(XMAX-XMIN)*DBLE(DSRND1D())
YI(I) = YMIN+(YMAX-YMIN)*DBLE(DSRND1D())
ZI(I) = ZMIN+(ZMAX-ZMIN)*DBLE(DSRND1D())
U(I) = XI(I)**2 + YI(I)**2 + ZI(I)**2
10 CONTINUE
C
C  Create the output grid.
C
DO 102 I=1,NX
XO(I) = XMIN+(DBLE(I-1)/DBLE(NX-1))*(XMAX-XMIN)
102 CONTINUE
C
DO 103 J =1,NY
YO(J)= YMIN+(DBLE(J-1)/DBLE(NY-1))*(YMAX-YMIN)
103 CONTINUE
C
DO 104 K=1,NZ
ZO(K) = ZMIN+(DBLE(K-1)/DBLE(NZ-1))*(ZMAX-ZMIN)
104 CONTINUE
C
C  Interpolate.
C
CALL DSGRID3D(NUM,XI,YI,ZI,U,NX,NY,NZ,XO,YO,ZO,OUTPUT,IER)
IF (IER .NE. 0) THEN
WRITE(6,520) IER
520   FORMAT(' Error ',I3,' returned from DSGRID3D')
STOP
ENDIF
C
C  Pass single precision arrays for plotting an isosurface.
C
DO 105 I=1,NX
XP(I) = XO(I)
DO 106 J=1,NY
YP(J) = YO(J)
DO 107 K=1,NZ
ZP(K) = ZO(K)
OUTP(I,J,K) = OUTPUT(I,J,K)
107     CONTINUE
106   CONTINUE
105 CONTINUE
C
C  Draw plot.
C
CALL GOPKS (IERRF, ISZDM)
CALL GOPWK (IWKID, LUNIT, IWTYPE)
CALL GACWK (IWKID)
CALL TDEZ3D(NX, NY, NZ, XP, YP, ZP, OUTP, 3.0, 0., 0., 0., 6)
CALL GDAWK (IWKID)
CALL GCLWK (IWKID)
CALL GCLKS
C
STOP
END
REAL FUNCTION DSRND1D()
C
DATA ISEED/1/
SAVE ISEED
C
ISEED = ISEED*1103515245 + 12345
IT = IAND(ISHIFT(ISEED,-16),32767)
C
DSRND1D = REAL(IT)/32767.
C
RETURN
END
```

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