Exponential decay functionSource:
expo_decay() can be used to increase or decrease a function exponentially
over iterations. This can be used to dynamically set parameters for
acquisition functions as iterations of Bayesian optimization proceed.
An integer for the current iteration number.
The number returned for the first iteration.
The number that the process converges to over iterations.
A coefficient for the exponent to control the rate of decay. The sign of the slope controls the direction of decay.
Note that, when used with the acquisition functions in
tune(), a wrapper
would be required since only the first argument would be evaluated during