Numerical methods for parabolic PDEs have been studied for many years.
A great deal of the research focuses on the stability problem in the
time integration of the systems of ODEs which result from the spatial
discretization. These systems often are stiff and highly expensive to
serve due to a huge number of components, in particular for multi-spac
e dimensional problems. The combination of stiffness and problem size
has led to an interesting variety of special purpose time integration
methods. In this paper we review such a class of methods, viz. explici
t Runge-Kutta methods possessing extended real stability intervals.