I have a system that looks like

```
dn/dt=f(n,v)
dh/dt=g(h,v)

```

I want to solve this equation on the manifold `F(v,n,h)=0`, a nonlinear function in `v`. I tried to use something like `v=fzero(@(x) F(x,n,h),0)` to solve for the value of v on the manifold at each time step. But this is incredibly slow and ode15s (my system is a relaxation oscillator) fails to meet integration tolerance. How do I find solution to the ODE on the manifold defined by `F(v,n,h)=0`?