SCREEN 12
VIEW (1, 40)-(638, 328), 8, 4                 'Grey box, red border
WINDOW (0, 0)-(10, 40)                        'Scale 0 to 10, 0 to 40
LINE (0, 0)-(10, 0), 9                        'Axis in bright blue

PRINT "Now a similar simulation allows a `live input' to perturb it"
PRINT "Press number keys 0 to 9 to change the input"
'
dt = .00002           'Make dt larger if you want to speed up running
k = .5
x = 10                                     'Initial value
t = 0
PSET (0, 10)
DO
   a$ = INKEY$                             'These two lines turn a
   IF a$ <> "" THEN u = 2 * VAL(a$)        'key-press into a value for u
     
   x = x + (-k * x + u) * dt               'This is the simulation
   t = t + dt
   LINE -(t, x)                            'This displays the result
LOOP UNTIL t > 10