Monday, April 15, 2024

LP in statistics: The Dantzig Selector

Lots of statistical procedures are based on an underlying optimization problem. Least squares regression and maximum likelihood estimation are two obvious examples. In a few cases, linear programming is used. Some examples are:

  • Least absolute deviation (LAD) regression [1]
  • Chebyshev regression [2]
  • Quantile regression [3]
Here is another regression example that uses linear programming. 

We want to estimate a sparse vector \(\color{darkred}\beta\) from the linear model \[\color{darblue}y=\color{darkblue}X\color{darkred}\beta+\color{darkred}e\] where the number of observations \(n\) (rows in \(\color{darkblue}X\)) is (much) smaller than the number of coefficients \(p\) to estimate (columns in \(\color{darkblue}X\)) [4]: \(p \gg n\). This is an alternative to the well-known Lasso method [5].

Friday, April 12, 2024

Instead of integers use binaries

In [1], a small (fragment of a) model is proposed:

High-Level Model
\[\begin{align} \min\> & \sum_i | \color{darkblue}a_i\cdot \color{darkred}x_i| \\ & \max_i |\color{darkred}x_i| = 1 \\ & \color{darkred}x_i \in \{-1,0,1\} \end{align}\]

Can we formulate this as a straight MIP?