# Difference between revisions of "STEM Solvers"

Line 4: | Line 4: | ||

|} | |} | ||

− | When you create a new scenario in STEM, you need to specify which solver to use. A solver is simply the method used to determine how the state of a simulation changes from one time step to the next. Models for populations and diseases in STEM are all designed to carry out this change or | + | When you create a new scenario in STEM, you need to specify which solver to use. A solver is simply the method used to determine how the state of a simulation changes from one time step to the next. Models for populations and diseases in STEM are all designed to carry out this change or derivative calculation given a current state. How the derivative is applied to determine the next state is where solvers differ. |

== Available solvers == | == Available solvers == | ||

=== Finite Difference === | === Finite Difference === | ||

− | The finite difference solver | + | The finite difference solver is the most straightforward (and most efficient) solver available. It's using Euler's method and simply estimates the next parameter value from the current value plus the derivative: |

+ | |||

+ | y(t+h) = y(t) +h*y'(t) | ||

[[Image:FiniteDifferenceFigure.png|800px]] | [[Image:FiniteDifferenceFigure.png|800px]] | ||

=== Runge Kutta Cash-Karp === | === Runge Kutta Cash-Karp === | ||

=== Dormand Prince === | === Dormand Prince === |

## Revision as of 17:13, 12 January 2012

When you create a new scenario in STEM, you need to specify which solver to use. A solver is simply the method used to determine how the state of a simulation changes from one time step to the next. Models for populations and diseases in STEM are all designed to carry out this change or derivative calculation given a current state. How the derivative is applied to determine the next state is where solvers differ.

## Available solvers

### Finite Difference

The finite difference solver is the most straightforward (and most efficient) solver available. It's using Euler's method and simply estimates the next parameter value from the current value plus the derivative:

y(t+h) = y(t) +h*y'(t)