# \bra

Used in Dirac bra-ket notation to denote a bra vector in quantum mechanics expressions.

https://texform.dev/latex/commands/bra

## Metadata

| Field | Value |
| --- | --- |
| Topic | [Physics: bra-ket](https://texform.dev/latex/topics/physics-braket) |
| Packages | braket, physics |
| Allowed mode | math |
| Tags |  |
| Commonality | low |
| Kind | prefix |

## Syntax

### braket

Argument specification: `m`

Used in Dirac bra-ket notation to denote a bra vector in quantum mechanics expressions.

### physics

Argument specification: `s m`

Used to denote a bra vector in quantum mechanics.

## Examples

```latex
\bra a
```

[Open in Playground](https://play.texform.dev/?input=%5Cbra+a)

```latex
\bra{a}
```

[Open in Playground](https://play.texform.dev/?input=%5Cbra%7Ba%7D)

```latex
\bra*{\psi}
```

[Open in Playground](https://play.texform.dev/?input=%5Cbra*%7B%5Cpsi%7D)

## Package variants

| Package | Argument specification | Allowed mode | Description |
| --- | --- | --- | --- |
| braket | m | math | Used in Dirac bra-ket notation to denote a bra vector in quantum mechanics expressions. |
| physics | s m | math | Used to denote a bra vector in quantum mechanics. |

## Renderer support

| Package | MathJax | KaTeX | XeTeX |
| --- | --- | --- | --- |
| braket | full | full | none |
| physics | full | full | full |

## In TeXForm

TeXForm parses this entry as prefix syntax; the package determines its argument specification.

### Expands to (braket)

```latex
\bra{#1}
```

→

```latex
{\langle {#1} \vert}
```

MathJax reads #1 with GetArgument, so a single token can be used without braces.

### Expands to (physics)

```latex
\bra{#1}
```

→

```latex
\left\langle{#1}\right\vert{}
```

If starred (\bra*{#1}), expands to \langle{#1}\vert. If immediately followed by \ket{...}, merges into a combined bra-ket representation.

### [physics/physics-bra-expand](https://texform.dev/rules/physics/physics-bra-expand)

Expand bra to an explicit angle-bracket and bar fence form.

Level: faithful. Fidelity: render.

```latex
\bra{#1}
```

→

```latex
\left\langle #1 \right\vert
```

```latex
\bra{\psi} H
```

→

```latex
\left\langle \psi \right\vert H
```

## Equivalent forms

```latex
{\langle {#1} \vert}
```

exact. 

```latex
\langle #1 \vert
```

approximate. Equivalent to the starred form \bra*{#1}.

```latex
\left\langle #1 \right\vert
```

approximate. Equivalent to the unstarred form, ignoring the trailing empty group.

## See also

- [\\bmod](https://texform.dev/latex/commands/bmod)
- [\\bmqty](https://texform.dev/latex/commands/bmqty)
- [\\boxed](https://texform.dev/latex/commands/boxed)
- [\\Bra](https://texform.dev/latex/commands/Bra)
- [\\flatfrac](https://texform.dev/latex/commands/flatfrac)
- [\\iff](https://texform.dev/latex/commands/iff)
- [\\imathbb](https://texform.dev/latex/commands/imathbb)
- [\\imathbfbb](https://texform.dev/latex/commands/imathbfbb)
- [\\impliedby](https://texform.dev/latex/commands/impliedby)
- [\\implies](https://texform.dev/latex/commands/implies)
- [\\itextbb](https://texform.dev/latex/commands/itextbb)
- [\\itextbfbb](https://texform.dev/latex/commands/itextbfbb)
- [\\jmathbb](https://texform.dev/latex/commands/jmathbb)
- [\\jmathbfbb](https://texform.dev/latex/commands/jmathbfbb)
- [\\jtextbb](https://texform.dev/latex/commands/jtextbb)
- [\\jtextbfbb](https://texform.dev/latex/commands/jtextbfbb)
- [\\ket](https://texform.dev/latex/commands/ket)
- [\\Ket](https://texform.dev/latex/commands/Ket)
- [\\ketbra](https://texform.dev/latex/commands/ketbra)
- [\\Ketbra](https://texform.dev/latex/commands/Ketbra)
- [\\LaTeX](https://texform.dev/latex/commands/LaTeX)
- [\\mathstrut](https://texform.dev/latex/commands/mathstrut)
- [\\matrixdeterminant](https://texform.dev/latex/commands/matrixdeterminant)
- [\\mdet](https://texform.dev/latex/commands/mdet)
- [\\mod](https://texform.dev/latex/commands/mod)
- [\\pmb](https://texform.dev/latex/commands/pmb)
- [\\pmod](https://texform.dev/latex/commands/pmod)
- [\\pmqty](https://texform.dev/latex/commands/pmqty)
- [\\Pmqty](https://texform.dev/latex/commands/Pmqty)
- [\\pod](https://texform.dev/latex/commands/pod)
- [\\qc](https://texform.dev/latex/commands/qc)
- [\\qcomma](https://texform.dev/latex/commands/qcomma)
- [\\Residue](https://texform.dev/latex/commands/Residue)
- [\\sbmqty](https://texform.dev/latex/commands/sbmqty)
- [\\skew](https://texform.dev/latex/commands/skew)
- [\\smdet](https://texform.dev/latex/commands/smdet)
- [\\spmqty](https://texform.dev/latex/commands/spmqty)
- [\\sPmqty](https://texform.dev/latex/commands/sPmqty)
- [\\stackbin](https://texform.dev/latex/commands/stackbin)
- [\\stackrel](https://texform.dev/latex/commands/stackrel)
- [\\substack](https://texform.dev/latex/commands/substack)
- [\\svmqty](https://texform.dev/latex/commands/svmqty)
- [\\TeX](https://texform.dev/latex/commands/TeX)
- [\\textbf](https://texform.dev/latex/commands/textbf)
- [\\textit](https://texform.dev/latex/commands/textit)
- [\\textnormal](https://texform.dev/latex/commands/textnormal)
- [\\textrm](https://texform.dev/latex/commands/textrm)
- [\\textsf](https://texform.dev/latex/commands/textsf)
- [\\texttt](https://texform.dev/latex/commands/texttt)
- [\\textup](https://texform.dev/latex/commands/textup)
- [\\varinjlim](https://texform.dev/latex/commands/varinjlim)
- [\\varliminf](https://texform.dev/latex/commands/varliminf)
- [\\varlimsup](https://texform.dev/latex/commands/varlimsup)
- [\\varprojlim](https://texform.dev/latex/commands/varprojlim)
- [\\vmqty](https://texform.dev/latex/commands/vmqty)
- [\\zeromatrix](https://texform.dev/latex/commands/zeromatrix)
- [\\zmat](https://texform.dev/latex/commands/zmat)

## Test cases

### braket

| Input | Case | MathJax | KaTeX | XeTeX |
| --- | --- | --- | --- | --- |
| \bra{a} | Positive: baseline | Pass | Pass | Fail |
| \bra a | Positive: bare[0] | Pass | Pass | Fail |

### physics

| Input | Case | MathJax | KaTeX | XeTeX |
| --- | --- | --- | --- | --- |
| \bra{a} | Positive: baseline | Pass | Pass | Pass |
| \bra*{a} | Positive: vary:s[0] | Pass | Pass | Pass |
| \bra a | Positive: bare[1] | Pass | Pass | Pass |