Calculate the Grantham Distance
A minimal set of routines to calculate the Grantham distance
. The Grantham distance attempts to
provide a proxy for the evolutionary distance between two amino acids
based on three key chemical properties: composition, polarity and
molecular volume. In turn, evolutionary distance is used as a proxy for
the impact of missense mutations. The higher the distance, the more
deleterious the substitution is expected to be.