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Let A be a Pedant and Let B be a Pedant

One of my favorite mathematical anecdotes is the following story that Gian-Carlo Rota told about Solomon Lefschetz: He [Solomon Lefschetz] liked to repeat, as an example of mathematical pedantry, the story of one of E. H. Moore’s visits to Princeton, when Moore started a lecture by saying, “Let a be […]

A Beautiful 2 by 2 Matrix Identity

While working on a variation of the RcppDynProg algorithm we derived the following beautiful identity of 2 by 2 real matrices: The superscript “top” denoting the transpose operation, the ||.||^2_2 denoting sum of squares norm, and the single |.| denoting determinant. This is derived from one of the check equations […]

A budget of classifier evaluation measures

Beginning analysts and data scientists often ask: “how does one remember and master the seemingly endless number of classifier metrics?” My concrete advice is: Read Nina Zumel’s excellent series on scoring classifiers. Keep notes. Settle on one or two metrics as you move project to project. We prefer “AUC” early […]