Eta (η) in LaTeX
In LaTeX maths mode, \eta produces the lowercase Greek letter eta (η). There is no separate command for uppercase Eta because it is identical to a Latin capital H, so you type H directly.
LaTeX command
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Eta is written \eta and must be used inside maths mode, for example between dollar signs. It renders as η, a lowercase letter that resembles a Latin n with a descending tail. Uppercase Eta looks exactly like a Roman H, so LaTeX offers no \Eta command; when you need it, simply type H, or \mathrm{H} for an upright roman shape.
Eta appears across the sciences. In fluid mechanics it denotes dynamic viscosity, in physics and engineering it marks efficiency, and in particle physics it is the pseudorapidity of a track. In machine learning it is the conventional symbol for a learning rate, and in number theory the Dedekind eta function is written \eta(\tau).
Because eta sits in maths mode it is italic by default, the standard convention for a variable. If you want an upright eta for a constant, load the upgreek package and use \upeta in a full LaTeX document; KaTeX and inline previews render the ordinary italic \eta without any package.
Other forms
\etalowercase etaExamples
$\eta$lowercase eta inline
$\eta = \frac{W_{\text{out}}}{W_{\text{in}}}$efficiency as a ratio of work
$\theta \leftarrow \theta - \eta \nabla L$a gradient-descent step with learning rate eta
$E = h\nu, \quad \eta = \frac{P_{\text{out}}}{P_{\text{in}}}$eta as an efficiency in physics
Tips and common mistakes
- There is no
\Etacommand; uppercase Eta is a Latin H, so type H, or\mathrm{H}for an upright capital. \etaonly works in maths mode; outside maths it is undefined and errors, so wrap it in .- Do not confuse
\eta(η) with a Latin n; eta has a distinctive descending tail. - For an upright eta representing a physical constant, use
\upetafrom the upgreek package; the default\etais italic. - In subscripts and superscripts eta behaves like any symbol, for example x_
\etaor e^{\eta}.
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Convert your maths to LaTeX →FAQ
How do I write a capital Eta in LaTeX?
There is no \Eta command because the uppercase Greek Eta is identical to the Latin capital H. Type H directly, or \mathrm{H} for an upright roman shape.
Why does \eta give an error?
\eta is only valid in maths mode. Enclose it in dollar signs, for example , or place it inside an equation environment.
What is eta used for in machine learning?
Eta (η) conventionally denotes the learning rate, the step size in gradient descent, as in \theta \leftarrow \theta - \eta \nabla L.