### Hopf initialization

The most natural way to start the continuation of a Hopf bifurcation curve is to start it from a Hopf point, typically found on an equilibrium curve. The continuation of Hopf points cannot simply be started by using the following command:
`[x,v,s,h,f]=cont(@hopf, x0, v0, opt)`
The Hopf curve file has to know

- the values of all state variables,
- which ode file to use,
- which parameters are active,
- the values of all parameters.

Also an initial point `x0` has to be known. All this information can be supplied using the following command:
`[x0,v0]=init_H_H(@odefile, xnew, p, ap)`.

The input arguments `odefile,` `xnew,` `p`, `ap` are built exactly as in `init_LP_LP`. The output vector `x0` consists of extended with the free parameters and paramter from (62).

MATCONT provides four other initializers which allow to continue a Hopf curve by starting from a codim 2 equilibrium point. These are `init_BT_H.m,` `init_GH_H.m`, `init_HH_H.m` and `init_ZH_H.m` These initializers are added merely for ease of use since they refer back to `init_H_H.m.` However, we note that two Hopf curves pass through a Hopf point. So it can be necessary to specify the tangent vector to the desired Hopf curve.