# Difference between revisions of "Running Your Model"

From Nova Documentation

(→Clock Settings) |
(→Clock Settings) |
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==Clock Settings== | ==Clock Settings== | ||

− | Once you have built a model but before you run it as a simulation, you must first set the clock parameters. | + | Once you have built a model but before you can run it as a simulation, you must first set the clock parameters. |

The clock settings consist of the following 4 parameters: | The clock settings consist of the following 4 parameters: | ||

*'''Start''' The time (in model time) when the simulation starts (this is usually 0). | *'''Start''' The time (in model time) when the simulation starts (this is usually 0). | ||

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*'''Integration Method''' The mathematical algorithm used to update Stocks and Variables. | *'''Integration Method''' The mathematical algorithm used to update Stocks and Variables. | ||

− | Nova currently uses an abstract unit of time that | + | Nova currently uses an abstract unit of time ("model time") that serves as the equivalent of some model-dependent real time unit (seconds, minutes, hours, days, years). |

'''Dt''', the increment, or "delta t", value, is the amount of time that elapses between State updates. For discrete models this is usually 1 (see below), but can be any value (0.1, 0.01, 0.05, 2, 20). | '''Dt''', the increment, or "delta t", value, is the amount of time that elapses between State updates. For discrete models this is usually 1 (see below), but can be any value (0.1, 0.01, 0.05, 2, 20). | ||

Nova supports 3 different integration methods | Nova supports 3 different integration methods | ||

+ | ;Euler | ||

+ | :Current state values are used in computations to determine the next state. Used for all discrete models. | ||

+ | ;RK2, RK4 | ||

+ | :These ''Runge-Kutta'' algorithms treat Stocks and Variables as continuous functions and reduce the error by subdividing the update interval. Simulations run slower but with more accuracy. RK4 is the preferred option of the two. | ||

+ | ;Discrete | ||

+ | :This is not actually an integration method; rather it sets '''Dt''' to 1 and uses the Euler method. The result is a sequence of State values rather than an attempt to approximate a continuous function. | ||

==Run Buttons== | ==Run Buttons== |

## Revision as of 21:15, 10 January 2015

This section describes how you run a model built with Nova's visual interface.

## Clock Settings

Once you have built a model but before you can run it as a simulation, you must first set the clock parameters. The clock settings consist of the following 4 parameters:

**Start**The time (in model time) when the simulation starts (this is usually 0).**End**The time (in model time) when the simulation ends.**Dt**The unit of increment (in model time) for updates.**Integration Method**The mathematical algorithm used to update Stocks and Variables.

Nova currently uses an abstract unit of time ("model time") that serves as the equivalent of some model-dependent real time unit (seconds, minutes, hours, days, years).

**Dt**, the increment, or "delta t", value, is the amount of time that elapses between State updates. For discrete models this is usually 1 (see below), but can be any value (0.1, 0.01, 0.05, 2, 20).

Nova supports 3 different integration methods

- Euler
- Current state values are used in computations to determine the next state. Used for all discrete models.
- RK2, RK4
- These
*Runge-Kutta*algorithms treat Stocks and Variables as continuous functions and reduce the error by subdividing the update interval. Simulations run slower but with more accuracy. RK4 is the preferred option of the two. - Discrete
- This is not actually an integration method; rather it sets
**Dt**to 1 and uses the Euler method. The result is a sequence of State values rather than an attempt to approximate a continuous function.