NAME

       gsw - simulate a three species individual-based ecosystem

SYNOPSIS

       gsw -help
         or
       gsw    [-width integer] [-height integer] [-steps integer]
              [-seed integer] [-plants integer] [-herbs  integer]
              [-carns  integer]  [-pmin  integer] [-pmax integer]
              [-Ep integer]  [-Eh  integer]  [-Ec  integer]  [-Ch
              integer]  [-Cc  integer] [-Pt integer] [-samp inte-
              ger]  [-stats]  [-pfreq  integer]  [-noext]  [-inv]
              [-mag integer] [-term string]

DESCRIPTION

       The  time  evolution  of an individual-based three species
       predator-prey ecosystem  is  simulated  according  to  the
       specified   parameters.   The  three  species  consist  of
       plants, herbivores,  and  carnivores  (grass,  sheep,  and
       wolves;  hence  the  name  GSW).   Updates  are  done syn-
       chronously, and each species has several parameters  which
       can  control  the  life  cycle,  from  the ability to give
       birth,  to  the  likelihood  of  starvation.    Population
       statistics  of  the three species can be calculated over a
       subset of the entire grid.

OPTIONS

       -width integer
              Width of the plot in pixels.

       -height integer
              Height of the plot in pixels.

       -steps integer
              Number of simulated steps.

       -seed integer
              Random seed for initial state.

       -plants integer
              Initial number of plants.

       -herbs integer
              Initial number of herbivores.

       -carns integer
              Initial number of carnivores.

       -pmin integer
              Minimum plants in vicinity to make new plant.

       -pmax integer
              Maximum allowed plants  in  vicinity  to  make  new
              plant.

       -Ep integer
              Energy of plant.

       -Eh integer
              Energy of herbivore.

       -Ec integer
              Energy of carnivore.

       -Ch integer
              Step energy cost for herbivores.

       -Cc integer
              Step energy cost for carnivores.

       -Pt integer
              Number of steps to grow plant.

       -samp integer
              Size of subsample statistaics.

       -stats Show statistics?

       -pfreq integer
              Plot frequency.

       -noext Prevent extinction?

       -inv   Invert colors?

       -mag integer
              Magnification factor.

       -term string
              How to plot points.

MISCELLANY

       An  interesting  change  to this code would involve making
       the the updates asynchronous, which would avoid some  sub-
       tle deadlock conditions that can occur in how the critters
       move.  Moreover, the motion of the  overall  system  would
       probably be more "lifelike".

BUGS

       No  sanity  checks  are performed to make sure that any of
       the options make sense.

AUTHOR

       Copyright (c) 1997, Gary William Flake.

       Permission granted for any use according to  the  standard
       GNU ``copyleft'' agreement provided that the author's com-
       ments are neither modified nor removed.   No  warranty  is
       given or implied.