Downsampling the Training Data =
Downsampling is a very simple way to improve the efficiency of your evolutionary runs. It might allow for deeper evolutionary searches and a greater success rate.
Using Downsampled selection with propeller is easy:
Set the :parent-selection argument to whichever selection strategy you would like, and set the :downsample? argument to true as follows:
lein run -m propeller.problems.simple-regression :parent-selection :lexicase :downsample? true <required downsampling args here>
The number of evaluations is held constant when comparing to a full training set run, so set the :max-generations to a number of generations that you would have gone to using a full sample.
Downsample Functions
In this repository, you have access to 3 different downsampling functions. These are the methods used to take a down-sample from the entire training set.
To use them, add the argument :ds-function followed by which function you would like to us
The list is - :case-maxmin - This is the method used for informed down-sampled lexicase selection - :case-maxmin-auto - This method automatically determines the downsample size - :case-rand- Random Sampling
Using :case-maxmin:
In order to use regular informed down-sampled selection, you must specify a few things: - :downsample-rate- This is the $r$ parameter: what proportion of the full sample should be in the down-sample $\in 0,1$ - :ds-parent-rate - This is the $\rho$ parameter: what proportion of parents are used to evaluate case distances $\in 0,1$ - :ds-parent-gens - This is the $k$ parameter: How many generations in between parent evaluations for distances $\in {1,2,3, \dots}$
Using :case-maxmin-auto:
In order to use automatic informed down-sampled selection, you must specify a few things: - :case-delta- This is the $\Delta$ parameter: How close can the farthest case be from its closest case before we stop adding to the down-sample - :ids-type - Either :elite or :solved - Specifies whether we are using elite/not-elite or solved/not-solved as our binary-fication of case solve vectors. - :ds-parent-rate - This is the $\rho$ parameter: what proportion of parents are used to evaluate case distances $\in 0,1$ - :ds-parent-gens - This is the $k$ parameter: How many generations in between parent evaluations for distances $\in {1,2,3, \dots}$
Using :case-rand:
In order to use regular randomly down-sampled selection, you must specify a few things: - :downsample-rate- This is the $r$ parameter: what proportion of the full sample should be in the down-sample $\in 0,1$
Here’s an example of running informed downsampled lexicase selection with $r=0.1$, $\rho=0.01$ and $k=100$ on the simple classification problem:
lein run -m propeller.problems.simple-classification :parent-selection :lexicase :downsample? true :ds-function :case-maxmin :downsample-rate 0.1 :max-generations 300 :ds-parent-rate 0.01 :ds-parent-gens 100