# Pearson Similarity

Algorithm link: Approximate Nearest Neighbors

The Pearson correlation coefficient is a measure of linear correlation between two sets of data. It is the ratio between the covariance of two variables and the product of their standard deviations. The formula for calculating the Pearson correlation coefficient is as follows:

\[\rho _{X,Y}={\frac {\operatorname {cov} (X,Y)}{\sigma _{X}\sigma _{Y}}}\]

The algorithm takes two vectors denoted by `ListAccum`

and returns the
overlap coefficient between them.

## Notes

This algorithm is implemented as a user-defined function. Follow the steps in Add a User-Defined Function to add the function to GSQL. After adding the function, you can call it in any GSQL query in the same way as a built-in GSQL function.