Brian Borchers
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 Mar 28 awarded Yearling Jan 27 comment Polytopes defined by $x_i >=0, Ax = b$ are generic ? (Understanding simplex method) Yes, any vertex will have at least $(n-r)$ zero components. However, if a vertex is degenerate then an arbitrarily small change to $A$ or $b$ can result in a change to the topology of polyhedron (e.g. new vertices and edges can appear.) Jan 27 comment Polytopes defined by $x_i >=0, Ax = b$ are generic ? (Understanding simplex method) No, there could be more than $n-r$ components that are 0. Such a vertex and basic feasible solution are called "degenerate." Jan 27 answered Polytopes defined by $x_i >=0, Ax = b$ are generic ? (Understanding simplex method) Jan 4 comment Linear vs non-linear Least Squares Note that it is possible to solve a linear least squares problem by solving a linear system of equations (the normal equations) or by using an orthogonal factorization of $A$ (QR or SVD.) Nonlinear least squares problems are solved by iterative methods. Dec 28 comment Calculate the Gamma function Γ(2.7) Your TI-83 PLUS probably can't do this. However, it's easy to evaluate using Wolfram Alpha. wolframalpha.com Dec 28 answered Calculate the Gamma function Γ(2.7) Dec 17 answered How to create an example with exponential running time for a given implementation of the simplex algorithm? Mar 9 answered Why can we assume a certain term is $0$ in this case? Mar 1 answered how to calculate variance on SVD parameter estimation? Sep 24 awarded Autobiographer May 16 comment What's wrong with this linear program formulation? Yes, you need to do some kind of phase I procedure to get a BFS. May 16 answered What's wrong with this linear program formulation? Sep 23 revised Difference between validity and satisfiability? Fixed an "A" vs. "F" typo Sep 23 comment Difference between validity and satisfiability? Note that the term "valid" is also commonly used as an adjective to describe a proof in the propositional calculus. If you consider an expression in the propositional calculus to be a one line proof, then a tautology (an expression that is true under all assignments of the logical variables) is a valid proof. Sep 23 answered Difference between validity and satisfiability? Jun 28 answered Quadratic integer Programming May 4 awarded Editor May 4 revised What does it mean to integrate with respect to the distribution function? expanded the explanation. May 4 answered What does it mean to integrate with respect to the distribution function?