Define additional math operators to be typeset in roman

Question

Mathematical operators, such as function names, should be set in roman type, not italics. Latex already has commands for some operators, including \max, \min, and \log. How can I define additional such commands?

Answer 1

\DeclareMathOperator{\foo}{foo} and \DeclareMathOperator*{\hocolim}{hocolim} for sub- and superscripts in the limits position.

Answer 2

Alternatively, if you are using any of the packages from the AMS (amsart.cls or amsmath.sty) then there is a command \DeclareMathOperator which does what it says on the tin! For example,

\DeclareMathOperator{\Det}{Det}

I think that it can handle variants, but I don't recall off the top of my head.

Answer 3

Define the command \newoperator as follows:

\providecommand{\newoperator}[3]{%
  \newcommand*{#1}{\mathop{#2}#3}}

Here is an example that defines \FD as an operator:

\newoperator{\FD}{\mathrm{FD}}{\nolimits}

Answer 4

If you're looking for something one-off, you can always use \mathrm in a math environment like so:

\mathrm{ultimatefunction}(x)

Which will display 'ultimatefunction' in a roman type.