IDENTIFICATION DIVISION
PROGRAM-ID TwoRaindrops
VERSION 20240201
COMMENT Two raindrops of same size and altitude are falling from a cloud.
COMMENT How long does it take until the touch?
COMMENT s'' = -2*gamma*m/s^2

ENVIRONMENT DIVISION
ENGINE Anabrid-THAT
TIMEBASE 1ms
REQUIRES COEFFICIENT 3, INVERTER 1, INTEGRATOR 2, COMPARATOR 1, MULTIPLIER 2, OPEN-AMP 1 

DATA DIVISION
OUTPUT OUTPUT.X s_limited
COEFFICIENT.1 MIN_DISTANCE  # 2*radius of the raindrop
COEFFICIENT.2 INIT_DISTANCE # initial distance -s0
COEFFICIENT.3 FACTOR        # 2*gamma*m

PROGRAM DIVISION
+1 -> COEFFICIENT.MIN_DISTANCE -> 2r
2r -> INVERTER -> -2r
-1 -> COEFFICIENT.INIT_DISTANCE -> -s0
+1 -> COEFFICIENT.FACTOR -> 2gamma*m
s'' -> INTEGRATOR -> -s'
-s', IC:-s0 -> INTEGRATOR -> s

# The raindrops may only approach until they touch. Our model does not include their unification
A:s, B:-2r, GT0:s, LT0:2r -> COMPARATOR -> s_limited

s_limited,s_limited -> MULTIPLIER -> s^2

# division 2gamma*m / s^2
# Open amplifier is realized on THAT by FB:SUMMER.GND -> SUMMER
2gamma*m, inp2 -> OPEN-AMP -> -2gamma*m/s^2=s''
2gamma*m^2, s^2 -> MULTIPLIER -> inp2

OPERATION DIVISION
MODE REPEAT
OP-TIME 12ms