Triangle Equal in LaTeX (\triangleq)

Where it is used

Equals sign topped with a small triangle, read is defined as.

Signal processing, control theory and information theory papers often prefer \triangleq for definitions, as in H(X) \triangleq -\sum p(x) \log p(x). It plays the same role as := but is symmetric, so it does not indicate which side is new. Some readers find it unfamiliar, so mention the convention once in the notation section. Alternatives include \stackrel{\text{def}}{=} or \overset{\mathrm{def}}{=}, and \equiv in physics. It is a relation, so spacing is automatic. Spell out the convention for any reader outside your field.

Also listed under: Computer Science

Minimal compilable example

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

\documentclass{article}
\usepackage{amssymb}
\begin{document}
Triangle Equal: $\triangleq$

\[ H(X) \triangleq -\sum_{x} p(x) \log p(x) \]
\end{document}

Related symbols

• Defined As:=
• Asymptotic\asymp
• Succeeds or Equal\succeq
• Precedes or Equal\preceq
• Succeeds\succ
• Precedes\prec

Frequently asked questions

How do I write Triangle Equal in LaTeX?

Type \triangleq in math mode, for example $H(X) \triangleq -\sum_{x} p(x) \log p(x)$. Load amssymb first with \usepackage{amssymb}.

Which package do I need for \triangleq?

\triangleq needs amssymb: add \usepackage{amssymb} to your preamble before the document starts.

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

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