model-builder(1) | General Commands Manual | model-builder(1) |

Model Builder is a graphical ODE simulator. It allows the user to

define, simulate and analyze arbitrary systems of Ordinary Diferential

Equations.

define and run your models. Just type-in you differential equations * Graphic output of simulation. You can save the graphics in the most

common formats: png, svg, pdf, etc. * Spreadsheet view of the results. From the spreadsheet you can make

customized plots from your variables. You can also export your data

to a .csv text file * Latex rendering of your system of equations. Check you equation in

clear mathematical notation. * Intuitive graphical interface. * Uncertainty analysis module. Implements a straightforward interface

for the Bayesian Melding method. * Sensitivity analysis. Find out how sensitive your model is to

variations in parameter values.

The best way to get started with ModelBuilder is open one of the

models included with the distribution and look at it . Yes, it's that

simple.

So, if you have already intalled it, start Model-Builder by typing in

the console:

$ PyMB followed by <enter>.

This will start Model-Buider . From now on I will assume that you

know what a system of differential equations is, otherwise you

probably should not be using Model-Builder.

The larger box on the main frame, labeled "Differential Equations" is

where we are going to start. On this text box you will write your

system of equations (or a single equation) The syntax is that of

python for mathematical expressions and functions and there are some

conventions also, which I will explain below: * First of all, Model-Builder expects only the right-hand-side (RHS)

of you equations to be present one per line in the equations

box. The LHS is assumed to be of the form dy(t)/dt, dy_i/dt where i

is an index to the the number of equations in your model. This

number i will be used to refer to the state variables of the model (

y[i] ). This index, i, MUST start at 0, so if your model has 3

equations, their state variables will be y[0], y[1], and y[2] . * Another convention is the reference to model parameters. Any number

of parameters may be included in the equations by the using this

nomeclature: p[0], p[1], and so on. These parameter must the be

specified one per line and in ascending order in the "Parameters"

box. So the first line would be the definition of p[0], the second

of p[1] and so forth. * The mathematical expressions that make up the equations and the

parameters may include any function of the numpy python module. This

allows for the easy contruction of models with a level of

sophistication higher than that of a simple algebraic

expression. Time may be referenced in the equations or parameter

expressions by the variable "t". So if you want a parameter that is

a function of time, you can simply write in the parameter box. * The user familiar with python will also be able to include more

advanced structures in the model specification, such as Lambda

functions for instance.

Well, with that out of the way, it remains to explain the rest of

the interface which is pretty much self-explanatory: * The initial values box should include one number for each equation

(line) in the equations box. The numbers should be separated by

spaces. * The start time is the time value at which the equations begin to be

evaluated. The values of the state variables at this point in time

are those specified in the initial conditions. * End time: You can figure this one out... * Time step: this is the time-step used in reporting the output of the

simulation. The actual time step used by the numeric integrator is

variable and chosen on the fly. Its normally much finer that what

you specify here. * Critical time steps. Most user wil leave this box empty. * First Step: The size of the first step. Leave at 0 for automatic

determination. * Min Step Size and Max Step Size: Respectively the minimum and

maximum value for step sizes as chosen by variable step size

algorithm. Leave at zero for automatic determination. * Full Output check box: If this box is checked a lot of useful

information about the integration is included in the output. Check

out the output spreadsheet to see what they are. * Show convergence message: if this box is checked, ModelBuilder will

print "Integration successful" to the console after the integration

is completed. Useful for debugging purposes only. Uncheck if you are

doing uncertainty analyses. as it will slow things down. * Once you are done entering the necessary information for you model,

Just press the start button to calculate your model. Enjoy!

This manual page was written by Varun Hiremath

<varunhiremath@gmail.com>, for the Debian project (but may be used by

others).

December 4, 2006 | Debian Sid |