Problem with NonNegative option of ODE45

Hi everyone!

I'm tryng to solve an implicit system of ordinary differential equation of the type:

where are some parameters. The problem is that if the resulting y is the ode solution ends up to be complex. In order to avoid this I''ve tried to add the option NonNegative to the ode solver. I've a sistem of 5 differential equation so i've written:

options = odeset('NonNegative',[1:5]);

But it does not work because I still find complex solution. Wat's wrong?

Thanks in advance!

[Davide Masiello]

Hi Luca - I would recommend to add your code.

[Torsten]

Maybe your differential equations are such that the solution variables become negative.

E.g. The differential equation dy/dt = -1 with y(0) = 1 has solution y(t) = -t+1 and it will become negative if t>1. The NonNegative option won't prevent this from happening.

The NonNegative option only might help if the variables become negative because of inaccuracies of integration.

[James Tursa]

Please show the actual equations.