Value of Hubble Parameter in Decelerating Universe

[Chalnoth]

During inflation the scale factor behaves as a \propto e^{Ht} and during a radiation dominated era it behaves as a \propto t^{1/2} and then during a matter dominated era behaves as a \propto t^{2/3}.

So then is it correct to say that during inflation: H= \dot{a}/a \propto constant
radiation dominated era: H= \dot{a}/a \propto 1/t
matter dominated era: H= \dot{a}/a \propto 1/t
from simply taking the derivative and dividing by a?

Does the Hubble parameter behave as 1/t during these eras? How would you find how it behaves during an era with mixed conditions, such as the present?

Thanks!

Not easily. Basically you'd have to go back to evaluate the integrals numerically (they can't be solved by hand).