[Tex/LaTex] ISO: cross product

isosymbols

ISO norms specify a standard symbol for cross product?

I found in many books of mathematics the

\times

operator, while in physics it seems widely used the

 \wedge

(or \land or another similar symbol?) operator.

Which is the correct one according to ISO norms?

Best Answer

The standard ISO 80000-2, “Mathematical signs and symbols to be used in the natural sciences and technology”, specifies that the symbol for vector product (commonly known as cross product, too) is “×” MULTIPLICATION SIGN U+00D7. This corresponds to \times in LaTeX.

The “wedge” symbol “∧” denotes “logical and” by that standard and in common practice in formal logic. Using it for other purposes is thus nonstandard and potentially misleading.

Related Solutions

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I stumbled upon the correct markup used in Wikipedia's article on geometric algebra. I looked at the code and found the symbol is given by \lrcorner. \llcorner is the same thing but flipped horizontally.

[Tex/LaTex] A \(re)newcommand that does not care if a command is already defined

There is \providecommand that defines a macro if it is not yet defined. Together with \renewcommand you have your "\extranewcommand":

\providecommand{\foo}{}
\renewcommand{\foo}[1]{bar: #1}

Or you can switch to the plain TeX primitives (other syntax!), e.g.:

\long\def\foo#1{bar: #1}

(\renewcommand and friends without star use \long\def and if the star form is given, \def without \long is used. Also the parameters are specified differently.)

`\declarecommand`

A definition of the "requested" \declarecommand that calls \providecommand and \renewcommand together:

\documentclass{article}

\makeatletter
\newcommand*{\declarecommand}{%
  \@star@or@long\declare@command
}
\newcommand*{\declare@command}[1]{%
  \provide@command{#1}{}%
  % \let#1\@empty % would be more efficient, but without error checking
  \renew@command{#1}%
}
\makeatother

\begin{document}

\declarecommand*{\foo}{\typeout{foo 1: \meaning\foo}}
\foo
\declarecommand{\foo}{\typeout{foo 2: \meaning\foo}}
\foo
\declarecommand*{\foo}[1]{\typeout{foo #1: \meaning\foo}}
\foo{3}

\end{document}

Result:

foo 1: macro:->\typeout {foo 1: \meaning \foo }
foo 2: \long macro:->\typeout {foo 2: \meaning \foo }
foo 3: macro:#1->\typeout {foo #1: \meaning \foo }