---- Shuffle Tester ----

I was curious what sorts of shuffles (on a deck of cards) worked best - and how many shuffles are needed to get a deck that is "well shuffled".

Currently, I only have one type of shuffle implemented (the classic Riffle shuffle).

To assess how shuffled a deck is, we use Spearman's Correlation. Where ρ is labeled as "Shuffle Precision" here.

Since we don't care about the directionality, we use |ρ|.

When ρ is close to 1, the deck is more unshuffled.

When ρ is close to 0, the deck is more shuffled.

From my tests, ρ bottoms out around 0.11 - 0.12

Note: the server running the code isn't super powerful. 1000 decks shuffled 20 times (each) takes about 25 seconds.