### Mathematics

SIR model and other models

Sensitivity and Specificity

- What is the probability that a person has the disease after he was tested positive?
- What is the probability that a person does not have the disease after she was tested negative?

Linear Optimization

The linear optimization is explained on a practical industrial case. The Simplex Algorithm is presented. The Excel Solver is described.

Earth Coordinates

I describe the Earth-centered (ECEF) cartesian and spherical coordinates as well as local ENU coordinates. I also derive transformations between them.

Great Circle on the EarthI derive the equation of the great circle on the spherical Earth, the formula for the shortest distance and other related formulas.

Torus

I derive equations of the torus and present an Octave program to draw it.

Zero-knowledge Proof

I present a simple zero-knowledge proof of map coloring with 3 colors.

Mathematics Stack Exchange

My contributions to Math.Stackexchange.