The FRONT section is used to define additional criteria for use by the adaptive regridder. In the normal case, FlexPDE repeatedly refines the computational mesh until the estimated error in the approximation of the PDE's is less than the declared or default value of ERRLIM. In some cases, where meaningful activity is confined to some kind of a propagating front, it may be desirable to enforce greater refinement near the front. In the FRONT section, the user may declare the parameters of such a refinement.
The FRONT section has the form:
FRONT ( criterion, delta )
The stated criterion will be evaluated at each node of the mesh. Cells will be split if the values at the nodes span a range greater than (-delta/2, delta/2) around zero.
That is, the grid will be forced to resolve the criterion to within delta as it passes through zero.