10 REM IBM
20 REM FORYIELD (Yield of forest plantation)
30 CLS
40 SCREEN 1, 0: COLOR 15, 0
50 LINE (0, 0)-(319, 180), 1, B
60 LINE (0, 80)-(319, 80), 1
70 J0 = 1
80 P1 = .016524
90 P2 = 1
100 P3 = .2
110 SW = 2
120 W = 100
130 M = 10
140 TW = 2000
150 TC = 200
160 K0 = .00283
170 K1 = .66
180 K2 = .05
190 K3 = .000066
200 K4 = .03
210 K5 = 1
220 K6 = .2
230 K7 = .4
240 K8 = .01
250 K9 = .00065
255 L1 = .05
260 DT = .1
270 T0 = 5
280 M0 = 2
290 W0 = .02
300 S0 = 20
310 PSET (T * T0, 180 - W * W0), 3
320  PSET (T * T0, 80 - M * M0), 1
330 PSET (T * T0, 160 - SW * S0), 2
340 G = K6 * M / P3
350  IF W > TW THEN X = 1
360  IF W < TC THEN X = 0
370 R = J0 / (1 + K0 * SW * W)
380 DW = K1 * R * SW * W - K2 * W - X * K5 * W
390 DS = K8 * G - K3 * R * SW * W - K4 * SW
400 DM = X * K5 * P1 * W - X * K9 * W * P2 - K9 * M - L1 * M - K6 * M
410 SW = SW + DS * DT
420  IF SW < 0 THEN SW = 0
430 W = W + DW * DT
440  IF W < 10 THEN W = 10
450 M = M + DM * DT
460 T = T + DT
470  IF T * T0 < 319 GOTO 310
480  LOCATE 2, 2: PRINT "Foryield.bas": SLEEP: SLEEP: END