**Figure 1: **A graphical illustration of the properties of three different penalty
functions. The eclipses represent the contours of the objective functions (A-C). The square, round, and star shapes represent the lasso, ridge, and bridge
constraint, respectively. The dots are the points where contours are “tangent”
to the constraints, i.e., the regularized estimates. Note that, in lasso (A) or
bridge (C), the constraint is discontinuous at zero. If the contour first touches
the constraint at point zero, the corresponding parameter estimate is zero and
variable selection is achieved [34]. |