In the toolbox fold curves are computed by minimally extended defining systems
cf. [22], §4.1.2.
The fold curve is defined by the following system
 |
(55) |
where
, while
is obtained by solving
 |
(56) |
and
are chosen such that the matrix in
(56) is nonsingular.
An advantage of this method is that the derivatives of
can be obtained
easily from the derivatives of
:
where
is a state variable or an active parameter and w is obtained by solving
 |
(57) |
This method is implemented in the curve definition file limitpoint.m.