### Torus bifurcation initialization

One way to start a continuation of torus bifurcations of cycles supported in the current version is to start it from a torus bifurcation point or neimarksacker point (NS) on a limit cycle curve. This can be done using the following command: `[x0,v0]=init_NS_NS(@odefile, x, s, ap, ntst, ncol)`. `x` should be the `x` as returned by the previous limit cycle continuation. `s` is the special point structure of the detected torus bifurcation point on the limit cycle curve. `odefile` specifies the ode-file to be used. `ap` is the array containing the two active parameters and `ntst` and `ncol` are again the number of mesh and collocation points for the discretization.

MATCONT provides seven other initializers to start the continuation of torus bifurcations from codim2 bifurcations of limit cycles. These all have the form `init_XYX_NS` where `XYX` is one of {CH,LP,PD,R1,R2,R3,R4}. They are introduced for ease of use since they all refer back to `init_NS_NS.m`.

More interesting and indeed nontrivial initializers are `init_HH_NS1.m,` `init_HH_NS2.m` and `init_ZH_NS.` Indeed, two different torus bifurcation curves can generically cross a HH point. Computational methods to switch to nonhyperbolic cycles from codim 2 bifurcations of equilibria are discussed in [29].