We consider a heat equation with a non-linear right-hand side which depends
on certain Volterra-type functionals. We analyse the question of convergen
ce for some finite difference schemes by means of discrete inverse formulae
instead of a maximum principle. It is due to this new technique that one c
an efficiently approximate these heat transport and diffusion-reaction equa
tions which require some functional (delayed-integral) values of the gradie
nt, too. Numerical experiments confirm our theoretical analysis and encoura
ge engineers to apply difference schemes to parabolic equations and systems
.