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Predator - Prey Dynamics - Rats and Snakes (Lotka Volterra Simulation)


Screen Shots:



User Instructions:


The simulator consists of three regions, the simulator's Viewable window, the Value-variable menu and the Simulation control menu.


The User Window:



The Value Variables Menu:



The values entered in 'Variables' Menu are default values. User can change the values according to the Data to be tested (try to study with different values for the parameters!).



The Variable Menu Contains:


  1. The prey-predator type.
  2. The drop down menu where the user can choose;


  • Time domain representation of r.
  • Prey to predator population.
  • Population to time ratio of Prey.
  • Population to time ratio of Predator.



The 'Initial rat population' tab can be used to enter the starting or initial population number/count of the rat (prey) population being studied.



The 'Initial snake population' tab can be used to enter the starting or initial population number/count of the snake (predator) population being studied.



The 'Number of steps' tab provides the user the option to run the simulator in as many steps he/she wishes to run.



The 'Step size' tab provides the user to reduce the number of steps given in the previous tab in terms of the step size given in this tab, for example say if number of step is 10 and the step size is 10 then the simulation could be over in just one step, if the step size is given as 1. For the same number of steps as in previous case if the step size was given as 1 then simulation would have finished in 10 steps only.




From the next button onwards are the tools for 'Simulation Control',



'Go to step' button with the tab helps to run the simulator directly to calculate population for the entered value for step number in the same tab.



'Step run' button is meant for manually running the simulator, step by step (in accordance to the values given in step size). For example, if the models population in every 0.1year is to be calculated, in each Step run, the model population's possible change for every 0.1 year is calculated and produced.



'Run Iterations', as the word means, runs the simulator slowly step by step with the same previously entered values repeatedly till the T time, can also be paused in between to get the values at the corresponding, desired time.



'Play/pause' button as in all cases is for pausing (and continuing) the simulator at any step needed while performing Iterations (slowly, repeatedly calculating the population possible in each step).



The 'Reset' button resets the simulator to the default values.



The 'Viewable Window' has some additional buttons meant for various other purposes,
The 'Statistics' button meant for viewing the time varying change in population by each step for the entered values in the simulator.
A sample for the 'User Window' when checked for the 'Statistics' could be,



Can be checked in case of any type of model.
The next is the 'Data plots' button having a graph symbol, on clicking will change the 'Viewable Window' to a graphical plot.



A sample:

On moving the arrow key over the graph, user can find the time and the exact population at the same time.
The 'Work sheet' button is meant for mathematical calculation using equations (which the simulator would do automatically). On clicking the button the 'Viewable Window' will change to a window similar to a calculation board, where the user can enter the required step in the 'At step' tab and simultaneously the population tab 'P' will get filled with the exact population value at the particular step with respect to the studying model type.




If by mistake the user checks for the plot of a model when he/she had not 'Run Iterations' then the simulator automatically will show a new popup window making alerts:



The simulator has a few draw backs like, there always has to be a considerably large difference between the Prey and the predator population values being entered, i.e., the prey population must be very high compared to the predator population.
The number of steps being entered shouldn't be too small; neither should the value be too large. The simulator may crash, depending on the value entered. This also depends on the power of the system being used.





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