Chris Kim: writingExplainers, notes, and TILs on numerical methods, quant, and software.https://chriskim.dev/Why stiff equations break explicit solvers: an interactive tour of stability regionshttps://chriskim.dev/writing/stiff-equations/https://chriskim.dev/writing/stiff-equations/Drag hλ across the complex plane and watch forward Euler explode while backward Euler barely notices. The test equation, amplification factors, and why stiffness depends on the step size you can afford.Mon, 28 Sep 2026 00:00:00 GMTRendering math at build time, so pages ship no math JavaScripthttps://chriskim.dev/writing/til-katex-astro/https://chriskim.dev/writing/til-katex-astro/remark-math and rehype-katex turn every equation on this site into HTML during the build. The browser only needs a stylesheet.Mon, 14 Sep 2026 00:00:00 GMTThe deflated Sharpe ratio, derived for people who tried 312 strategieshttps://chriskim.dev/writing/deflated-sharpe/https://chriskim.dev/writing/deflated-sharpe/My best pairs-trading variant had a Sharpe ratio of 0.31. After accounting for the 311 others, the probability it beats luck is 0.18. Each step of Bailey and López de Prado’s correction, derived and checked with real numbers.Thu, 20 Aug 2026 00:00:00 GMTnp.einsum won’t find a cheaper contraction order unless you askhttps://chriskim.dev/writing/til-einsum-path/https://chriskim.dev/writing/til-einsum-path/One keyword argument made a three-operand contraction in Kestrel about 27× faster.Sat, 11 Jul 2026 00:00:00 GMTExpected rolls until two sixes in a row (it's 42), three wayshttps://chriskim.dev/writing/two-sixes/https://chriskim.dev/writing/two-sixes/First-step equations, a casino full of fair gamblers, and a million simulated games. Why the answer is 42 and not 36, and where the extra 6 comes from.Sat, 02 May 2026 00:00:00 GMTCP-SAT solution hints: start from the plan the student already hashttps://chriskim.dev/writing/til-cpsat-hints/https://chriskim.dev/writing/til-cpsat-hints/Passing a student's previous plan to CP-SAT as a hint halved Prereq's median re-plan solve time.Sat, 28 Mar 2026 00:00:00 GMT