Implementing a basic predator-prey simulation

I am trying to implement a predator-prey simulation, but I am running into a prob开发者_如何学编程lem. A predator searches for nearby prey, and eats it. If there are no near by prey, they move to a random vacant cell.

Basically the part I am having trouble with is when I advanced a "generation."

Say I have a grid that is 3x3, with each cell numbered from 0 to 8.

If I have 2 predators in 0 and 1, first predator 0 is checked, it moves to either cell 3 or 4

For example, if it goes to cell 3, then it goes on to check predator 1. This may seem correct but it kind of "gives priority" to the organisms with lower index values.. I've tried using 2 arrays, but that doesn't seem to work either as it would check places where organisms are but aren't. ._.

Anyone have an idea of how to do this "fairly" and "correctly?"

I recently did a similar task in Java. Processing the predators starting from the top row to bottom not only gives "unfair advantage" to lower indices but also creates patterns in the movement of the both preys and predators.

I overcame this problem by choosing both row and columns in random ordered fashion. This way, every predator/prey has the same chance of being processed at early stages of a generation.

A way to randomize would be creating a linked list of (row,column) pairs. Then shuffle the linked list. At each generation, choose a random index to start from and keep processing.

More as a comment then anything else if your prey are so dense that this is a common problem I suspect you don't have a "population" that will live long. Also as a comment update your predators randomly. That is, instead of stepping through your array of locations take your list of predators and randomize them and then update them one by one. I think is necessary but I don't know if it is sufficient.

This problem is solved with a technique called double buffering, which is also used in computer graphics (in order to prevent the image currently being drawn from disturbing the image currently being displayed on the screen). Use two arrays. The first one holds the current state, and you make all decisions about movement based on the first array, but you perform the movement in the other array. Then, you swap their roles.

Edit: Looks like I didn't read your question thoroughly enough. Double buffering and randomization might both be needed, depending on how complex your rules are (but if there are no rules other than the ones you've described, randomization should suffice). They solve two distinct problems, though:

• Double buffering solves the problem of correctness when you have rules where decisions about what will happen to a creature in a cell depends on the contents of neighbouring cells, and the decisions about neighbouring cells also depend on this cell. If you e.g. have a rule that says that if two predators are adjacent, they will both move away from each other, you need double buffering. Otherwise, after you've moved the first predator, the second one won't see any adjacent predator and will remain in place.
• Randomization solves the problem of fairness when there are limited resources, such as when a prey only can be eaten by one predator (which seems to be the problem that concerned you).

How about some sort of round robin method. Put your predators in a circular linked list and keep a pointer to the node that's currently "first". Then, advance that first pointer to the next place in the list each generation. You could insert new predators either at the front or the back of your circular list with ease.