With a suitably chosen bounded
domain
$\Omega\subset \mathbb R^2$, we
consider the Dirichlet problem
for
a scalar reaction-diffusion
equation of the form $ u_t = \Delta u + f(u),
t>0, x \in \Omega.
$ We show that there is a nonempty set G of functions $f$, that is
open
in a $C^1$ topology and such that for
any
$f\in G$ the following
situation occurs. The above equation has two
hyperbolic equilibria
$\phi$, $\psi$ such that their
stable and unstable manifolds
$W^s(\psi)$ and $W^u(\varphi)$ intersect nontransversally.
This
shows
that the transversality of stable and
unstable
manifolds is not a
generic property in the class of spatially homogeneous
equations.
In
contrast, this property is generic if
nonlinearities
of the form
$f=f(x,u)$ are considered (this was shown by Brunovsky and
Polacik). In one space dimension, the
transversality
occurs always (not
only generically), as shown in
independent
works of Henry and
Angenent.