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Example relevant for the exercises

In order to understand the relation among the predictors p , the set of data n and the target (outcome, output etc) \boldsymbol{y} , we condiser a simple polynomial fit. We assume our data can represented by a fourth-order polynomial. For the $i$th component we have

\tilde{y}_i = \beta_0+\beta_1x_i+\beta_2x_i^2+\beta_3x_i^3+\beta_4x_i^4.

we have five predictors/features. The first is the intercept \beta_0 . The other terms are \beta_i with i=1,2,3,4 . Furthermore we have n entries for each predictor. It means that our design matrix is an n\times p matrix \boldsymbol{X} .