Kappa in LaTeX (\kappa)

Where it is used

Lowercase Greek kappa, used for curvature, condition numbers, and Cohen's kappa.

Differential geometry writes the curvature of a curve as \kappa = |\gamma''(s)|, and numerical analysis uses \kappa(A) = \|A\|\|A^{-1}\| for the condition number of a matrix. Statistics has Cohen's \kappa for inter-rater agreement, and physics uses it for thermal conductivity or the dielectric constant. The variant \varkappa gives a different glyph some authors prefer. There is no \Kappa command because capital kappa is identical to Latin K. Do not swap \kappa with the Latin k, since many formulas use both.

Minimal compilable example

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

\documentclass{article}
\begin{document}
Kappa: $\kappa$

\[ \kappa(A) = \|A\|\,\|A^{-1}\| = \frac{\sigma_{\max}}{\sigma_{\min}} \]
\end{document}

Related symbols

• Lambda\lambda
• Iota\iota
• Lambda (Upper)\Lambda
• Theta (Upper)\Theta
• Mu\mu
• Theta\theta

Frequently asked questions

How do I write Kappa in LaTeX?

Type \kappa in math mode, for example $\kappa(A) = \|A\|\,\|A^{-1}\| = \frac{\sigma_{\max}}{\sigma_{\min}}$. It works in plain LaTeX without loading any package.

Which package do I need for \kappa?

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

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

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