Statistics
Least squares, three ways
The normal equations, QR, and the SVD solve the same problem with very different accuracy. The difference is the square of a condition number.
Notebook: rerunning an analysis from two years ago
What it took to reproduce an old bootstrap analysis, and why its confidence interval moved in the third decimal place.
Why the sample variance divides by n − 1
A short proof that dividing by n − 1 removes the bias, and a reminder that the unbiased estimator is not the most accurate one.