Xi (Ξ ξ) in LaTeX
In LaTeX, \xi gives the lowercase xi (ξ) and \Xi gives the uppercase xi (Ξ), both used in maths mode.
LaTeX command
\XiNot the symbol you meant? Draw it to find the command →
Lowercase xi, \xi, is a flowing three-stroke letter often used as a dummy variable of integration, a spatial coordinate in a transformed frame, or a generic random variable in probability. In statistical physics it is the correlation length, and in analytic number theory the Riemann xi function is written \xi(s).
Uppercase xi, \Xi, is drawn as three stacked horizontal bars. It is less common but appears as the cascade baryon in particle physics and as a grand-potential or partition-function-like quantity in statistical mechanics. Type \Xi for the capital; both commands are maths-mode only.
Xi is one of the harder Greek letters to draw by hand, exactly the kind of symbol a handwriting-to-LaTeX tool resolves cleanly. Lowercase \xi is italic and uppercase \Xi upright by default; for a bold xi use \boldsymbol{\xi}. There is no \varxi variant in standard LaTeX.
Other forms
\xilowercase xi\Xiuppercase xi (Ξ)Examples
$\xi$lowercase xi inline
$\int f(\xi)\,d\xi$xi as a dummy variable of integration
$\Xi$uppercase xi
$\xi(s) = \tfrac{1}{2}s(s-1)\pi^{-s/2}\Gamma\!\left(\tfrac{s}{2}\right)\zeta(s)$the Riemann xi function
Tips and common mistakes
- Use
\xifor a dummy variable or random variable;\Xifor the three-bar capital. - There is no
\varxi; only\xiand\Xiexist. - Both are maths-mode only; wrap them in .
- For a bold xi use
\boldsymbol{\xi}, since\mathbfdoes not bold lowercase Greek letters. - Uppercase
\Xiis a plain letter; do not confuse it with the summation operator\sum.
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Convert your maths to LaTeX →FAQ
How do I write a capital xi in LaTeX?
Use \Xi, which renders Ξ as three horizontal bars. It appears in particle physics and statistical mechanics.
Is xi the same as the summation sign?
No. The summation operator is \sum, a distinct large symbol. Uppercase xi (\Xi) is three simple horizontal bars and is an ordinary letter.
What is xi commonly used for?
Lowercase xi (\xi) is a common dummy variable, coordinate or random variable, and in physics it denotes a correlation length.