# How to write a decay function in Python

At my exercise of reinforcement learning, I needed to write a decay function for Ɛ-greedy strategy. The mathematical function should look something like:

f(x) = decay^x

But in the algorithm, I don’t have access to the iterator value (x in the above formula), only the current epsilon (Ɛ) and the decay factor I defined.

It turns out it is not necessary to use x to obtain the same value. If `x` is the current step in the iteration, all that is needed to do is:

Ɛ = Ɛ * decay

It would translate to

Ɛ = Ɛ * decay ^ X

Where `X` would be the total amount of steps in the iteration. In python, the code would look like:

self.epsilon = self.epsilon * self.decay

Although simple, it took me some time to visualize both functions are equal but written in different forms.

## About The Author

Thiago Ricieri

I’m software engineer at Pluto TV, working on iOS, Android and Roku platforms. Personally interested in machine learning, algorithms, data science and tech industry. I travel a lot and take good pictures.