10 REM SPLINE
20 REM G.Seidl , 6/90
30 REM
40 N=20 : H=30
50 DIM Y(N)
60 REM
70 FOR I=0 TO N : READ Y(I) : NEXT
80 REM Me�punkte zeichnen
90 SCREEN 9 : CLS
100 FOR I=0 TO N
110 X=I*H : Y=Y(I)
120 LINE (X,Y)-(X,200)
130 NEXT
140 GOSUB 170
150 W$=INKEY$ : IF W$="" THEN 150
160 END
170 REM Splineberechnung
180 A1=(Y(1)-Y(0))/H : REM Anfangssteigung
190 FOR I=0 TO N-2 STEP 2
200 Y1=Y(I) : Y2=Y(I+1) : Y3=Y(I+2)
210 GOSUB 330 : REM Spline-Koeffizienten holen
220 FOR X=0 TO H
230 XX=X+I*H
240 YY=Y1+A1*X+B1*X^2+C1*X^3
250 PSET (XX,YY)
260 XX=H+X+I*H
270 YY=Y2+A2*X+B2*X^2+C2*X^3
280 PSET (XX,YY)
290 NEXT
300 A1=A2+2*B2*H+3*C2*H^2
310 NEXT
320 RETURN
330 REM Berechnung der Spline-Koeffizienten
340 D1=Y2-Y1:D2=Y3-Y2
350 A=(2*D2-3*D1)/H^2+A1/H
360 B2=2*A/3
370 C2=(-A/3)/H
380 B1=(3*D1-D2)/H^2-(2*A1/H)+A/3
390 C1=((D2-2*D1)/H^2+A1/H-A/3)/H
400 A2=A1+H*(2*B1+3*H*C1)
410 RETURN
415 REM y-Werte der Kurvenst�tzpunkte
420 DATA 100,100,100,110,130,120,100,090,070,050,100,120,100,100
430 DATA 130,150,160,150,130,100,100