Mark,

interesting idea. Given the fact that in 2-d euclidean metric, the
Einstein summation conventions are only a way to write out
conventional matrix multiplications, do you consider at some point to
include a non-euclidean metric in this thing? (As you have in special
relativity, for example)

Something along the lines:

eta = np.diag(-1,1,1,1)

a = np.array(1,2,3,4)
b = np.array(1,1,1,1)

such that

einsum('i,i', a,b, metric=eta) = -1 + 2 + 3 + 4