### 20.2.4 Linear regression

Given a set of points (x0,y0),…,(xn−1,yn−1), linear regression finds the line y=mx+b that comes closest to passing through all of the points; i.e., that makes

√

(y0−(m x0+b))2+⋯+(yn−1−(m xn−1+b))2

as small as possible. The linear_regression command finds the linear regression of a set of points.

- linear_regression takes two arguments:
  - xcoords, a list of x-coordinates.
  - ycoords, a list of y-coordinates.
  You can combine two arguments into a matrix with two columns (each list becomes a column of the matrix).
- linear_regression(xcoords,ycoords) returns a sequence m,b of the slope and y-intercept of the regression line.

#### Example

linear_regression([[0,0],[1,1],[2,4],[3,9],[4,16]])

or:

linear_regression([0,1,2,3,4],[0,1,4,9,16])

4,−2 |  |  |  |  |  |  |  |  |  |

which means that the line y=4x−2 is the best fit line.

The linear_regression_plot command draws the best fit line.

- linear_regression_plot takes two arguments:
  - xcoords, a list of x-coordinates.
  - ycoords, a list of y-coordinates.
  You can combine two arguments into a matrix with two columns (each list becomes a column of the matrix).
- linear_regression_plot(xcoords,ycoords) draws the line of best fit through the points. It will also give you the equation at the top, as well as the R2 value, which is

  R2=

  n−1
  ∑
  j=0

  (m xj+b−ȳ)2

  n−1
  ∑
  j=0

  (yj−ȳ)2

  (The R2 value will be between 0 and 1 and is one measure of how good the line fits the data; a value close to 1 indicates a good fit, a value close to 0 indicates a bad fit.)

#### Example

linear_regression_plot([0,1,2,3,4],[0,1,4,9,16])