Ps-i version 2.4 manual

About Ps-i 2.4.

Ps-i 2.2 is an environment for study of agent-based simulations.

The design of Ps-i 2.0 had the following goals in mind:

• the model implemented in the program should be changeable by end users
• 99% of the program's codebase should be shared between Windows and Linux (Unix) versions
• full functionality of the program should be available under Linux to facilitate fast development
• the featureset of the program should encompass the featureset of the first version.

To achieve these goals the following design decisions were made:

• the model description is external to the program and is contained in model configuration file (usually with extension ".mdl")
• the user interface was implemented using Tcl/Tk library which allowed all of the code (except for two startup files) to be shared between Linux (Unix) and Windows versions
• the core of the model consists of the library of functions and the data related to the model being currently run; the dependencies between library functions are weak - that is they are due to the particular form of the data structures and not the algorithms implemented in the model.

Version 2.2 builds upon its precursor with several improvements:

• simplified model specification file syntax
• improved user interface
• ability to specify a number of parameters, easily changeable from user interface
• faster runs with routine optimization, speculative evaluation and JIT-compiler
• faster field display
• the ability to save and restore program runs
• the ability to import landscape files from Ps-i 1.0 and 1.5
• the ability to run Tcl/Tk scripts

The following improvements were incorporated in 2.4.0:

• selection tool allows to select areas using geometrical figures and mathematical expressions
• effect tool allows to change attributes of agents in the area created by selection tool according to user-defined expressions
• improved interactivity
• support for tcl scripts embedded in model specification files
• hash functions that can be used to generate repeatable random sequences
• templatized creation of new model specification files (ABIR model, currently)
• dynamic addition of attributes

Ps-i 2.4 model configuration file.

The model file consists of the following sections:

• Attributes section
• Agent classes section
• Fields section
• Routines section
• Rules section
• Views section
• Statistics section
• Miscellaneous commands - which can be put in any place in the file.

Model configuration files are commonly stored with extension .mdl.

It is generally recommended that a novice user takes an existing configuration file and use it as a template for constructing description of his/her model.

Note that the snapshot files (with extension .snp) have identical syntax, but are not meant to be edited by the end user.

Ps-i 2.4 scripting interface

Ps-i 2.4 has the ability to load Tcl/Tk scripts and execute scripts embedded in model specification files and snapshots. These files are commonly stored with extension .scp. All standard Tcl/Tk commands are available to the user. In addition, there are a number of commands specific to Ps-i 2.4:

• Tcl/Tk interface
• Embedded scripts