Probability simulation

Question

I have been asked to simulate whether a printer works after every hour in one day (i.e. 24 hours). If the printer works after the hour, then it has an 90% probability of working and 10% probability of being broken at the end of the next hour.

If broken, then it has 50% probability of working or being broken the next hour.

Assume random uniform distribution and that the first hour the printer is working.

My code in Python is below:

Chance = []
Status = []
for i in range(24):
    Chance.append(random.uniform(0,1))
Chance[0] = 1
Chance

for i in Chance:
    if i > 0.1:
        Status.append('Working')
    else:
        Status.append('Broken')
Chance, Status

My problem is I can't simulate the the current event based on the previous event, i.e. if the previous event is broken how can I adjust the probability of the current event to 0.5.

First, you can do Chance = np.random.uniform(size=24) instead of the for loop. Second, why do you have Chance on line 6 all by itself? — kevinkayaks

AlEmerich AlEmerich · Accepted Answer · 2019-01-15T05:50:04

You need to define your probability table before, like this:

                 |              NEXT STATE                |
                 |    WORKING        |      BROKEN        |
CURRENT| WORKING |      0.9          |        0.1         |
STATE  |---------|-------------------|--------------------| 
       | BROKEN  |      0.5          |        0.5         |

In order to be able to change the value very easily. You can even easily add new state. Use it like this:

import random

# The table above
table = [[.9,.1],[.5,.5]]

def simulate():
    # 0 means working, 1 means broken
    current_state = 0
    # Initialise variable
    next_state = current_state

    for i in range(24):
        # Get a number between 0 and 1
        chance = random.uniform(0, 1)

        # Given my current state (line 0 or 1), what chance do I have
        # to work the next hour ?
        if chance <= table[current_state][0]:
            # The chance variable has more chance to be under if the number
            # in the table is high.
            next_state = 0
        else:
            # BROKEN
            next_state = 1
        current_state = next_state
        print("Current state " + ("Working" if current_state == 0 else "Broken"))

if __name__ == "__main__":
    simulate()

Probability simulation

3 Answers