exercise2:
  Find best linear model for Playfair data.
  cost of wheat = c0 + c1 * year
  Data from playfair_data.txt involves n = 50 items with dimension d = 3
  Data statistics:
    Min      =  [1565.   26.    5.]
    Max      =  [1810.   99.   30.]
    Range    =  [245.  73.  25.]
    Mean     =  [1687.5      42.14     11.5816]
    Variance =  [5206.25        216.9704       52.74468944]
  Graphics saved as "exercise2_data.png"
  C =  [ 5.45468037e+01 -2.95284893e-02]
  MSE =  1.4859182006507448
  Graphics saved as "exercise2_fitted.png"

  The model predicts that in 1850, wheat will cost  -0.08090149530158897