# Cost function

## Introduction

In ML, cost functions are used to estimateFind an approximate value for an unknown quantity. how badly models are performing. Put simply, a cost function is a measure of how wrong the model is in terms of its ability to estimateFind an approximate value for an unknown quantity. the relationship between X and y. This cost function (you may also see this referred to as loss or error.) can be estimated by iteratively running the model to compare estimated predictions against “ground truth” — the known values of y^{[2]}

## A fairly decent video