# Example 1 - a simple 3D interpolation (Fortran single 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
REAL XI(NUM), YI(NUM), ZI(NUM), U(NUM)
REAL XO(NX),  YO(NY),  ZO(NZ),  OUTPUT(NX,NY,NZ)
INTEGER I, J, K, IER
DATA XMIN,YMIN,ZMIN,XMAX,YMAX,ZMAX / -2., -2., -2., 2., 2., 2./
C
DO 10 I=1,NUM
XI(I) = XMIN+(XMAX-XMIN)*DSRND1()
YI(I) = YMIN+(YMAX-YMIN)*DSRND1()
ZI(I) = ZMIN+(ZMAX-ZMIN)*DSRND1()
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+(REAL(I-1)/REAL(NX-1))*(XMAX-XMIN)
102 CONTINUE
C
DO 103 J =1,NY
YO(J)= YMIN+(REAL(J-1)/REAL(NY-1))*(YMAX-YMIN)
103 CONTINUE
C
DO 104 K=1,NZ
ZO(K) = ZMIN+(REAL(K-1)/REAL(NZ-1))*(ZMAX-ZMIN)
104 CONTINUE
C
C  Interpolate.
C
CALL DSGRID3S(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 DSGRID3S')
STOP
ENDIF
C
C  Plot an isosurface.
C
C
C Open GKS and define the foreground and background color.
C
CALL GOPKS (IERRF, ISZDM)
CALL GOPWK (IWKID, LUNIT, IWTYPE)
CALL GACWK (IWKID)
C
CALL TDEZ3D(NX, NY, NZ, XO, YO, ZO, OUTPUT, 3.0,
+            2., -35., 65., 6)
CALL FRAME()
C
C Close GKS.
C
CALL GDAWK (IWKID)
CALL GCLWK (IWKID)
CALL GCLKS
C
STOP
END
REAL FUNCTION DSRND1()
C
DATA ISEED/1/
SAVE ISEED
C
ISEED = ISEED*1103515245 + 12345
IT = IAND(ISHIFT(ISEED,-16),32767)
C
DSRND1 = REAL(IT)/32767.
C
RETURN
END
```

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