implicit DAE using ode15i

Dear all, I have an implicit Differential algebraic equation that I used ode15i to solve. However, I know the solutions should be real numbers but instead I get a complex part of the magnitude of 1e-20 with each solution. Now, how could that happened? what does that complex part mean? and how do I force the ode15i function to look for real solution? Thanks for any help!

Answer 1

[lei shi]

I find it is not easy to use like ode45 ,I am solve daes too .