``Fastest''
requires the definition of a norm.
Considerations of norms and their connection to kinetics
can be found in,
Carter W.C, Taylor J.E., and Cahn J.W.,
``Variational methods for microstructural-evolution theories''
Journal of Materials, pp 30-36 (1997).
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.