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WHAT IS MONTE CARLO SIMULATION?
What do we mean by "simulation?"
When we use the word simulation, we refer to any analytical method meant to imitate a real-life system, especially when other analyses are too mathematically complex or too difficult to reproduce.
Without the aid of simulation, a spreadsheet model will only reveal a single outcome, generally the most likely or average scenario. Spreadsheet risk analysis uses both a spreadsheet model and simulation to automatically analyze the effect of varying inputs on outputs of the modeled system.
One type of spreadsheet simulation is Monte Carlo simulation, which randomly generates values for uncertain variables over and over to simulate a model.
How did Monte Carlo simulation get its name?
Monte Carlo simulation was named for Monte Carlo, Monaco, where the primary attractions are casinos containing games of chance. Games of chance such as roulette wheels, dice, and slot machines, exhibit random behavior.
The random behavior in games of chance is similar to how Monte Carlo simulation selects variable values at random to simulate a model. When you roll a die, you know that either a 1, 2, 3, 4, 5, or 6 will come up, but you don't know which for any particular roll. It's the same with the variables that have a known range of values but an uncertain value for any particular time or event (e.g. interest rates, staffing needs, stock prices, inventory, phone calls per minute).
What do you do with uncertain variables in your spreadsheet?
For each uncertain variable (one that has a range of possible values), you define the possible values with a probability distribution. The type of distribution you select is based on the conditions surrounding that variable. Distribution types include: triangular, uniform , normal and Longomal distributions
To add this sort of function to an Excel spreadsheet, you would need to know the equation that represents this distribution. With Crystal Ball, these equations are automatically calculated for you. Crystal Ball can even fit a distribution to any historical data that you might have.
What happens during a simulation?
A simulation calculates multiple scenarios of a model by repeatedly sampling values from the probability distributions for the uncertain variables and using those values for the cell. Your simulations can consist of as many trials (or scenarios) as you want - hundreds or even thousands - in just a few seconds.
During a single trial, your simulator randomly selects a value from the defined possibilities (the range and shape of the distribution) for each uncertain variable and then recalculates the spreadsheet.
You may also check this document explaining all kinds of simulations in Orcad including the monte carlo simulation
**broken link removed**
The Monte Carlo/yield analysis capabilities can be used to study the effects of statistical variations on circuit performance...used to analyze the yield of a circuit for a given description of the statistical properties of the component values.
There are two steps that need to be performed before analyzing the yield of a circuit. The first is setting up the parameter value statistical properties. The second is the specification of the goals used to determine if a circuit has acceptable (pass) or unacceptable (fail) performance.
This helps assess the reliability and improve the production yield of the circuit.
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