2' 'ư>HELPNA\NhNN:l CONTINUE n((PAEXIT&%p=lHALTމPl dSTEP 1 4߉lg STOP߉X^F%EFSTOP ,,OFFg^w@߉UT߉WO6gp߉.Od6Bg|߉6B|ŻOdg6BModelsPredator.gpsLFeCFEOthLthFhE(((((((((({\rtf1\ansi\deff0\deftab720{\fonttbl{\f0\fswiss MS Sans Serif;}{\f1\froman\fcharset2 Symbol;}{\f2\fmodern Courier New;}} {\colortbl\red0\green0\blue0;} \deflang1033\pard\tx1200\tx2400\tx4450\plain\f2\fs20 ; GPSS World Sample File - PREDATOR.GPS \par ****************************************************************** \par * * \par * Lotka-Volterra Predator-Prey Model * \par * * \par * Operation: * \par * Plot Foxes and Rabbits: X 12000; Y 0-3000 * \par * START 1 * \par ****************************************************************** \par \par \par ****************************************************************** \par * \par * Don't forget to parenthesize the ODEs. \par * \par ****************************************************************** \par Foxes\tab INTEGRATE\tab (FoxRate()) \par Rabbits\tab INTEGRATE\tab (RabbitRate()) \par \par ****************************************************************** \par * \par * The Initial Values \par * \par ****************************************************************** \par Foxes\tab EQU\tab 80 \par Rabbits\tab EQU\tab 1000 \par \par ****************************************************************** \par * \par * The Model Parameters \par * \par ****************************************************************** \par K_\tab EQU\tab 0.2000\tab ;Predator Efficiency \par A_\tab EQU\tab 0.0080\tab ;Predator Death Rate \par B_\tab EQU\tab 0.0002\tab ;Foray (Grazing) Factor \par C_\tab EQU\tab 0.0400\tab ;Prey Birth Rate \par \par ****************************************************************** \par * * \par * Discrete Simulation Control Segment * \par * * \par ****************************************************************** \par \tab GENERATE\tab 10000 \par \tab TERMINATE\tab 1 \par \par \par PROCEDURE FoxRate() BEGIN \par /***************************************************************** \par Growth Rate for the Fox Population \par *****************************************************************/ \par \tab TEMPORARY BirthRate, DeathRate, TotRate; \par \tab \par /* Limit the Variable, so we can experiment safely. */ \par \tab IF (Foxes < 0) THEN Foxes = 0; \par \tab IF (Foxes > 10e50) THEN Foxes = 10e50 ; \par \par \tab BirthRate = K_ # B_ # Foxes # Rabbits; \par \tab DeathRate = A_ # Foxes; \par \tab TotRate = BirthRate - DeathRate; \par \tab \par \tab RETURN TotRate; \par END; \par \par \par PROCEDURE RabbitRate() BEGIN \par /***************************************************************** \par Growth Rate for the Rabbit Population \par *****************************************************************/ \par \tab TEMPORARY BirthRate, DeathRate, TotRate; \par /* Limit the Variable, so we can experiment safely. */ \par \tab IF (Rabbits < 0) THEN Rabbits = 0; \par \tab IF (Rabbits > 10e50) THEN Rabbits = 10e50 ; \par \par \tab BirthRate = C_ # Rabbits; \par \tab DeathRate = B_ # Foxes # Rabbits ; \par \tab TotRate = BirthRate - DeathRate; \par \par \tab RETURN TotRate; \par END; \par \par \par }