We now suppose that we have a gridded data set composed of a space-time field X(t, s)
representing the value of the field X, such as SLP, at time t and spatial position s.
The value of the field at discrete time ti and grid point sj
is noted xij for i = 1, . . . , n
and j = 1, . . . p = p1p2. The observed field is then represented by the data matrix: