Monte Carlo Simulation
Monte Carlo simulations are used to model the probability of different outcomes in a process that cannot
easily be predicted due to the intervention of random variables. It is a technique used to understand the
impact of risk and uncertainty in prediction and forecasting models.
A Monte Carlo simulation can be used to tackle a range of problems in virtually every field such as
finance, engineering, supply chain, and science. It is also referred to as a multiple probability simulation.
Monte Carlo Simulation History
Monte Carlo simulations are named after the popular gambling destination in Monaco, since chance and
random outcomes are central to the modeling technique, much as they are to games like roulette, dice, and
slot machines.
The technique was first developed by Stanislaw Ulam, a mathematician who worked on the Manhattan
Project. After the war, while recovering from brain surgery, Ulam entertained himself by playing
countless games of solitaire. He became interested in plotting the outcome of each of these games in order
to observe their distribution and determine the probability of winning. After he shared his idea with John
Von Neumann, the two collaborated to develop the Monte Carlo simulation.
Monte Carlo Simulation Method
The basis of a Monte Carlo simulation is that the probability of varying outcomes cannot be determined
because of random variable interference. Therefore, a Monte Carlo simulation focuses on constantly
repeating random samples to achieve certain results.
A Monte Carlo simulation takes the variable that has uncertainty and assigns it a random value. The
model is then run and a result is provided. This process is repeated again and again while assigning the
variable in question with many different values. Once the simulation is complete, the results are averaged
together to provide an estimate.
When a system contains elements that exhibit chance in their behavior, the Monte Carlo method of
simulation can be applied.
The basic idea in Monte Carlo simulation is to generate values for the variables making up the model
being studied. There are a lot of variables in real-world systems that are probabilistic in nature and that
we might want to simulate. A few examples of these variables follow
1. Inventory demand on a daily or weekly basis
2. Lead time for inventory orders to arrive
3. Times between machine breakdowns
4. Times between arrivals at a service facility
5. Service times 6. Times to complete project activities
7. Number of employees absent from work each day
Some of these variables, such as the daily demand and the number of employees absent, are discrete and
must be integer valued. For example, the daily demand can be 0, 1, 2, 3, and so forth. But daily demand
cannot be 4.7362 or any other no integer value. Other variables, such as those related to time, are
continuous and are not required to be integers because time can be any value. When selecting a method to
generate values for the random variable, this characteristic of the random variable should be considered.
Examples of both will be given in the following sections. The basis of Monte Carlo simulation is
experimentation on the chance (or probabilistic) elements through random sampling. The technique
breaks down into five simple steps.
Five Steps of Monte Carlo Simulation
1. Establishing probability distributions for important input variables
2. Building a cumulative probability distribution for each variable in step 1
3. Establishing an interval of random numbers for each variable
4. Generating random numbers
5. Simulating a series of trials