Exponential decay/growth and associated rates

[metric-space]

It seems like the exponential decay referred throughout and most likely used by library users is exponential growth rather exponential decay

Exponential decay has a negative exponent.

It would be nice to have a separation for the sake of correctness

That aside, would it not be nice for the exponential stuff to have constants associated with them? or is that beyond the scope of the project?

P.S As a matter of fact, none of the predefined decay functions are actually decaying, all of them are growth functions (double,exponential and golden-ratio)