This is purely a guess, but I think it's because all the exponents are scalar. You get exponents when the derivative of a function is proportional to itself:

This is purely a guess, but I think it's because all the exponents are scalar. You get exponents when the derivative of a function is proportional to itself: d/dx (f) = k*f So exponentials will be scalars because the exponential part is scaling the original value. Example: population growth is exponential. d/dt(p) = (ln(2)/r)*p p(t) = p0 * 2^(t/r) p : population p0: population t : days r : days (time it takes for the population to double) t/r : scalar