Time- and Space-Efficient Algorithms for Least Median of Squares Regression. Souvaine, D. L. & Steele, J. M. J Am Stat Assoc, 82(399):794–801, 1987.
abstract   bibtex   
The least median of squared residuals regression line (or LMS line) is that line $y = ax + b$ for which the median of the residuals $|y_i - ax_i - b|^2$ is minimized over all choices of $a$ and $b$. If we rephrase the traditional ordinary least squares (OLS) problem as finding the $a$ and $b$ that minimize the mean of $|y_i - ax_i - b|^2$, one can see that in a formal sense LMS just replaces a ``mean'' by a ``median.'' ṡ Two algorithms are given here that determine the LMS regression line for $n$ points in the plane, using $O(n^2 łog n)$ time and $O(n)$ space and $O(n^2)$ time $O(n^2)$ space, respectively.
@Article{souvaine87time,
  author   = {Diane L. Souvaine and J. Michael Steele},
  title    = {Time- and Space-Efficient Algorithms for Least Median of Squares Regression},
  journal  = {J Am Stat Assoc},
  year     = {1987},
  volume   = {82},
  number   = {399},
  pages    = {794--801},
  abstract = {The least median of squared residuals regression line (or LMS line) is that line $y = ax + b$ for which the median of the residuals $|y_i - ax_i - b|^2$ is minimized over all choices of $a$ and $b$. If we rephrase the traditional ordinary least squares (OLS) problem as finding the $a$ and $b$ that minimize the mean of $|y_i - ax_i - b|^2$, one can see that in a formal sense LMS just replaces a ``mean'' by a ``median.'' \dots Two algorithms are given here that determine the LMS regression line for $n$ points in the plane, using $O(n^2 \log n)$ time and $O(n)$ space and $O(n^2)$ time $O(n^2)$ space, respectively.},
  keywords = {phylogenetics},
}

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