This module applies to a plane curve $C$ the non-linear heat 
equation~\cite{gage.hamilton:heat}~\cite{grayson:heat}
\index{heat equation}
$$\frac{\partial C}{\partial t}(s,t) 
= \frac{\partial^2 C}{\partial s^2}(s,t),$$
($s$ being the arlength parameterization of the curve)
by alternatively convolving the function $s\mapsto C(s)$ with a
Gaussian kernel (see \verb+sgauss+ module) and reparameterizing it.
This algorithm is described in~\cite{mackworth.mokhtarian:theory}. 
With the \verb+-N+ option~\cite{mackworth.mokhtarian:scale-based}, 
no reparameterization is applied and the scheme
is not consistant any more with the mean curvature motion
\index{mean curvature motion}
$$\frac{\partial C}{\partial t}(s,t) = \kappa(s,t) \; N(s,t),$$
where $\kappa$ and $N$ are the local curvature and normal to the curve
$s\mapsto C(s,t)$.
