Solving ODE with conditional statements

Hi,

I have a question here regarding ODE modeling in matlab. I was wondering if I can create an ODE model with conditional statements.

For example: dx/dt = 1/7 dy/dt = 1/3 dy/dt = 0 if x & y are both integers

If it is possible, what would be the command/coding script for dy/dt in this case?

Thanks!

Answer 1

[Jan]

An integration requires a smooth function. For such discontinuities the stepsize controller of Matlab's integrators get serious troubles, see e.g. http://www.mathworks.com/matlabcentral/answers/59582#answer_72047 .

The integrator controls the stepsize based on the locale discretization error. Therefore it is very unlikely, that the variables are exactly integer. Then notice, that x and y will have integer values for an infinitely interval only. Therefore changing the derivative there, this cannot change the result of the integration.

Answer 2

[G]

For example if:

dx/dt = 1/2,

dy/dt = 1/4,

dy/dt = 0 if both x and y are intergers

at t = 0 [x,y] = [0,0]

Therefore, at t = 4, x = 2 and y = 1

So you're saying that MatLab's ODE Solver does not have the capability of drawing on a true/false mechanism to determine if both x and y are integers for the stepwise model of dy/dt?