Sigma (Upper) in LaTeX (\Sigma)

Where it is used

Uppercase Greek Sigma as a letter, used mainly for covariance matrices and alphabets.

In statistics \Sigma denotes a covariance matrix, as in \mathbf{x} \sim \mathcal{N}(\boldsymbol{\mu}, \Sigma), and the SVD writes A = U\Sigma V^\top. Formal language theory uses \Sigma for an alphabet and \Sigma^* for all strings over it. For summation, use \sum instead: \Sigma is an ordinary fixed-size letter that does not grow in display mode or carry limits. Complexity theory uses \Sigma_k^p for the polynomial hierarchy. Capital Greek letters are upright; \varSigma is the italic variant.

Minimal compilable example

Paste this into an empty .tex file and compile it with pdfLaTeX, XeLaTeX or LuaLaTeX.

\documentclass{article}
\begin{document}
Sigma (Upper): $\Sigma$

\[ A = U \Sigma V^{\top}, \quad \mathbf{x} \sim \mathcal{N}(\mu, \Sigma) \]
\end{document}

Related symbols

• Tau\tau
• Sigma\sigma
• Upsilon\upsilon
• Rho\rho
• Upsilon (Upper)\Upsilon
• Pi (Upper)\Pi

Frequently asked questions

How do I write Sigma (Upper) in LaTeX?

Type \Sigma in math mode, for example $A = U \Sigma V^{\top}, \quad \mathbf{x} \sim \mathcal{N}(\mu, \Sigma)$. It works in plain LaTeX without loading any package.

Which package do I need for \Sigma?

None. \Sigma is part of standard LaTeX, so it compiles with nothing in the preamble but the document class.

Can I use \Sigma in text mode, or only in math mode?

Only in math mode. Outside $...$ LaTeX stops with "Missing $ inserted", so write $\Sigma$ in running text. If you only need the glyph in text, paste the Unicode character Σ instead (with XeLaTeX or LuaLaTeX and a font that has it).