Eta in LaTeX (\eta)

Where it is used

Lowercase Greek eta, used for learning rates, efficiency, viscosity, and the Minkowski metric.

In machine learning \eta is the conventional learning rate in updates like w \leftarrow w - \eta \nabla L(w). Thermodynamics writes efficiency as \eta = W/Q_h, fluid dynamics uses it for dynamic viscosity, and relativity writes the Minkowski metric \eta_{\mu\nu}. Statistics sometimes uses it for the linear predictor \eta = X\beta of a generalized linear model. Capital eta looks like Latin H, so there is no \Eta command. Do not confuse \eta with the Latin n in sans-serif slides, where the descender may be hard to see.

Also listed under: Machine Learning & AI

Minimal compilable example

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

\documentclass{article}
\begin{document}
Eta: $\eta$

\[ w_{t+1} = w_t - \eta \nabla L(w_t) \]
\end{document}

Related symbols

• Theta\theta
• Zeta\zeta
• Theta (Upper)\Theta
• Epsilon (Variant)\varepsilon
• Iota\iota
• Epsilon\epsilon

Frequently asked questions

How do I write Eta in LaTeX?

Type \eta in math mode, for example $w_{t+1} = w_t - \eta \nabla L(w_t)$. It works in plain LaTeX without loading any package.

Which package do I need for \eta?

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

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

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