LaTeX: Cross-referencing between Different Documents

Problem: I have a manuscript TeX file (main.tex), and an independent supporting information file (si.tex). I was to cross-reference (using \label and \ref) items across the two files.

For example, I might want to reference figure 1 from si.tex in main.tex.

Solution: As this SO answer suggests, the answer lies in the CTAN package xr.

In main.tex, just include "si.tex" as an external documents, and all its labels become visible!

\usepackage{xr}
\externaldocument{si}

Parameter Uncertainty in Numpy Polyfit

Say you want to fit a line to (x,y) data. With polyfit, you can say,

coeff = np.polyfit(x, y, 1)

With numpy 1.7 and greater, you can also request the estimated covariance matrix,

coeff, cov = np.polyfit(x, y, 1, cov=True)

The standard error on the parameters is the square-root of the diagonal elements

print(np.sqrt(np.diag(cov)))

This report referenced in the SO page is quite useful!