COSESAI

Newton-Raphson Root Finder Field Guide: When One Tangent Outruns Bracketing, Bisection, and Secant in a Single Iteration

By xiezixing 2026年10月12日

Newton-Raphson doubles the digits you trust each step. Most root-finders trade one correct bit for…

Modular Arithmetic Calculator Field Guide: When Five Operations, One Bezout Identity, and the Bit-Length Rule Decide Whether Your Modular Computation Is Exact or a Free Estimate

By xiezixing 2026年9月23日

Modular arithmetic field guide: five operations (add, subtract, multiply, inverse, power) with BigInt precision up to 10^18. Walks through the extended Euclidean algorithm for inverse, square-and-multiply for power, and the canonical [0, m-1] representative.

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Permutation / Combination / Subset Generator (With Repeats) Field Guide: When Five Items, Six Rows, Three Modes, and One Display Cap Decide Whether Your Multiset Count Lands at n! or n!/Π(mᵢ!)

By xiezixing 2026年9月16日

Five items, six rows. Five items, six rows: that is the entire surprise of multiset…

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Multiset Counting Is Three Formulas — Permutation / Combination / Subset Generator Field Guide

By xiezixing 2026年9月10日

Counting distinct arrangements of repeated items is the kind of math that looks elementary until…

Biorhythm Curve Plotter poster: Three sine curves do not predict your day

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Three sine curves don’t predict your day: the 23/28/33 biorhythm chart and the three decisions that decide whether it’s worth opening

By xiezixing 2026年7月10日

The arithmetic is real, the prediction is not. Inside the 23/28/33-day chart: birth-date precision, the meaningless combined total, and why “critical day” happens ~79 times a year.