Use pdepe to solve an ode

Hi everyone,

I am using the pdepe splver to solve a set of 2 pdes that arou coupled and it works great. However, I now want to couple another equation, which does not have a flux term. Therefore, by the pdepe notation,

m = 0, c = 1, f = 0, and s = u-1 (the s is just an example, not my actual s).

The problem is that pdepe discretization supports only parabolic and elliptic equations, with flux term involving spatial derivative.

How can I couple all three equations if two equations are pdes and one equation is ode.

Thank you!

Answer 1

[Torsten]

So your equation is not a PDE, but a simple ODE.

Either you try to artificially set du/dx = 0 at both ends and see whether the results make sense.

Or you use Bill Greene's code who claims that ODEs can be handled therein.

Or - as you wrote that there is another problem with your equations that pdepe cannot handle (sigmoid function) - discretize your equations in space and use ODE15S to solve the resulting system of ordinary differential equations in the grid points. Look up "method-of-lines" for more details.