Math, Numerics, and Software My name is Reid Atcheson. I have a PhD in Computational and Applied Mathematics (CAAM) from Rice University. I am a senior technical consultant for Numerical Algorithms Group (NAG). I periodically write here about my interests. I have interest in the following: Scientific computation and numerical analysis High performance computing Correctness of numerical algorithms Functional programming Writing 23 Aug 2021 Model Reduction for a Parameterized Linear System 08 Mar 2021 Significant Performance Variation in Sparse LU Factorizations 26 Feb 2021 More Fun with Rust Iterators: Matrix-Matrix Multiply 07 Feb 2021 Visualizing Nested Dissection 07 Feb 2021 Nested Dissection for Sparse QR Factorization (video) 03 Feb 2021 Compressing the Sparse QR Factorization with Nested Dissection and Block Low-Rank Approximation 27 Jan 2021 An Interesting Inverse Inequality: Proof 24 Jan 2021 Conjecture Proven: New arXiv Manuscript Up 11 Jan 2021 Does QR Factorization Solve Linear Systems More Accurately Than Dense LU Factorization? 13 Nov 2020 Research in Progress: Nested Dissection Sparse QR Factorization 23 Oct 2020 Characterizing GMRES Convergence Part 1.4: Preconditioning Example 16 Oct 2020 Characterizing GMRES Convergence Part 1: Not Just Conditioning 21 Jul 2020 Waning Sars-Cov2 Immunity, Yet Another SIR Model 28 Apr 2020 Smoothing Covid19 Cases Data with Linear Programming 19 Oct 2019 Rust and C++ on Floating-point Intensive Code 18 May 2019 Recovering Sparsity from Noisy Data 21 Apr 2019 Fitting Noisy Data with Outliers 25 Mar 2019 Division Using only Multiply and Add 20 Mar 2019 7 Dubious Solutions to Approximate Floating-Point Equality 09 Mar 2019 Performance Results of Low-Rank Trick 03 Mar 2019 Quickly Discover Low-Rank Structure with GMRES 27 Feb 2019 Linear Algebra Secrets: Low Rank Updates 04 Aug 2018 I am a Below Average Quake Champions Player 26 May 2018 What to do when Julia's lufact runs out of memory 19 Mar 2018 Rice HPC Oil&Gas Conference 2018 15 Jan 2018 Estimating Errors in Summing Arrays of Floating Point Numbers 10 Jan 2018 Breaking Bayesian Inference 02 Jan 2018 Excluded Middle and the Stock Market 28 Dec 2017 Intermediate Value Theorem on Rational Numbers 14 Dec 2017 Computing Square Root of Rational Numbers 14 Nov 2017 Talk at SC17 02 Apr 2017 Rice HPC Oil&Gas Conference 22 Dec 2016 Abstract Numerical Linear Algebra: Update! 19 Oct 2016 Joint Post with Julia Computing 14 Oct 2016 Abstract Numerical Linear Algebra 27 Dec 2015 Running MPI Jobs on Google Compute Instances 07 Dec 2015 The danger of variable length arrays in C99+ 12 Jul 2015 An International Mathematical Olympiad Problem 23 Apr 2015 I am a doctor now 07 Dec 2014 Infinitude of Primes Revisited 29 Aug 2014 JuliaCon Presentation 06 Jul 2014 Reciprocal Sum of Primes Diverges 04 Jul 2014 Infinitely many prime numbers: Euler's proof 10 Jan 2014 First website.