Typesetting of negative versus minus?

Question

I've occasionally seen a negative (when a number is simply negative, not a subtraction), typeset as negative sign that's slightly skinnier and above the centre line of text. Is this proper notation for mathematics and how would one go about typesetting this in LaTeX?

Edit

I believe that calculators were what happened to give me this idea, couldn't find it in any of my math books. Thank you all for the help, it's much appreciated.

Thank you 'Antal S-Z' for the photo link.

However, the question remains, how exactly would I typeset this?

Answer 1

If latex gives you a binary minus and you want the unary minus (i.e. negative), just add curly braces around the expression, e.g. change -x to {-x}. See post #4 at mathhelpforum

Answer 2

My understanding is that a negative sign is the same as a minus sign, but the spacing is different since it's a unary operator rather than a binary operator. You can see this in TeX: $-x$ has different spacing from $y-x$:

I'm not sure I can answer your question about it being proper, but I'll say that I've never seen mathematics typeset with a raised, smaller negative sign. (But take that with a grain of salt because most, but not all, math I read is typeset with LaTeX.)

Answer 3

Here is an example, but you still have to distinguish between unary and binary minus manually:

\documentclass{minimal}

\usepackage{xparse}

\makeatletter
\NewDocumentCommand{\raisedminus}{m}{%
  \raisebox{0.2em}{$\m@th#1{-}$}%
}
\NewDocumentCommand{\unaryminus}{}{%
  \mathbin{%
    \mathchoice{%
      \raisedminus\scriptstyle
    }{%
      \raisedminus\scriptstyle
    }{%
      \raisedminus\scriptscriptstyle
    }{%
      \raisedminus\scriptscriptstyle
    }%
  }%
}
\makeatother

\begin{document}

$\unaryminus 3 - 4$

\end{document}

Answer 4

I'll throw in a few thoughts to answer the part "Is this proper notation for mathematics" of the question. First of all: No, it's not proper. One reason, as others have observed before me: It's just never used, except in school textbooks where they have to distiguish two different keys on the calculator keyboard. So, if you type a manual for a calculator, you can use Philipp's \unaryminus. (And otherwise you shouldn't use it.)

The second reason: Try to use the symbol in handwriting. Will you really manage to write it in a way that it is always clear which of two minus symbols is meant? At least I wouldn't. I think this is one of the reasons why in mathematics there is just this one minus sign.

What I can't answer is why they have two different keys on the calculator. Maybe it was for simplifying the programming in the early days, or it's for didactic reason; I don't know.

Answer 5

Here is a LuaLaTeX approach that discovers unary minuses automatically (but the \raisebox doesn't work for a reason I don't understand):

\documentclass{minimal}

\usepackage{luatextra}
\usepackage{xparse}

\makeatletter
\NewDocumentCommand{\raisedminus}{m}{%
  \raisebox{0.2em}{$\m@th#1{-}$}%
}
\makeatother

\newsavebox{\scriptraisedminus}
\sbox{\scriptraisedminus}{\raisedminus{\scriptstyle}}
\newsavebox{\scriptscriptraisedminus}
\sbox{\scriptscriptraisedminus}{\raisedminus{\scriptscriptstyle}}

\begin{luacode}
local unary_minus = node.new(15)
unary_minus.display = node.new(16, 0)
unary_minus.display.nucleus = node.new(32)
unary_minus.display.nucleus.list = node.copy_list(tex.getbox(\number\scriptraisedminus))
unary_minus.text = node.new(16, 0)
unary_minus.text.nucleus = node.new(32)
unary_minus.text.nucleus.list = node.copy_list(tex.getbox(\number\scriptraisedminus))
unary_minus.script = node.new(16, 0)
unary_minus.script.nucleus = node.new(32)
unary_minus.script.nucleus.list = node.copy_list(tex.getbox(\number\scriptscriptraisedminus))
unary_minus.scriptscript = node.new(16, 0)
unary_minus.scriptscript.nucleus = node.new(32)
unary_minus.scriptscript.nucleus.list = node.copy_list(tex.getbox(\number\scriptscriptraisedminus))

function is_bin_conv_to_ord(v, p)
  if not v or v.id \string~= 16 or v.subtype \string~= 4 then return false end
  if not p then return true end
  if p.id == 16 and ((p.subtype >= 1 and p.subtype <= 6) or p.subtype == 8) then return true end
  local n = v.next
  if q and q.id == 16 and (q.subtype == 5 or q.subtype == 7 or q.subtype == 8) then return true end
  return false
end

function replace_unary_minus(head, displaytype, need_penalties)
  local p = nil
  local v = head
  while v do
    if is_bin_conv_to_ord(v, p) then
      local n = v.nucleus
      if n and n.id == 31 and n.fam == 2 and n.char == 0 then
        node.insert_after(head, v, node.copy(unary_minus))
        head, w = node.remove(head, v)
      end
    end
    p = v
    v = v.next
  end
  return node.mlist_to_hlist(head, displaytype, need_penalties)
end

luatexbase.add_to_callback("mlist_to_hlist", replace_unary_minus, "replace_unary_minus")
\end{luacode}

\begin{document}

$-3 - 4$

\end{document}

Answer 6

I think it is a nice question, but...

The minus on the TI-84 as a negative number can be used in the input without brackets... So you can type: 3 + -5 and the calculator will not make a problem of it. But if you type 3 + -5 as a minus, than the calculator will jump to the error "-". (same for 3*-5=-15 and 3* "-"5 gives an error.

In order to show you the error on the calculator, there is a difference between the 2 characters on a calculator.

I don't see any reasons to make that difference in typing. Like said above... you don't make a difference in handwriting, why should you make it complex (and I dont mean complex numbers :-) in typing.

Let's go for the KIS method... Keep it simple.

As a bonus the code for TI-84 buttons

\documentclass{article}
\usepackage{graphicx}
\usepackage{fancybox}
%%FOR TI 84 buttons
\newcommand{\btb}[1]{\ovalbox{\rule[-0.5ex]{0pt}{2ex}{\tt #1}}}
\newcommand{\sel}[1]{{\tt [#1]}}
\newcommand{\bt}[1]{\btb{#1}\index{{\tt [#1]}}}
\newcommand{\sbt}[1]{\btb{2nd}{\sel{#1}}}
\newcommand{\abt}[1]{\btb{alpha}{\sel{#1}}}
\begin{document}
\begin{itemize}
    \item   \bt{3} \bt{+} \bt{-} \bt{5} \bt{=} \bt{-2}
    \item \bt{3} \bt{+} \bt{$-$} \bt{5} \bt{=} SYNTAX ERROR
\end{itemize}
\end{document}

Answer 7

I don't see this as a unary operator but more of a typesetting property of negative numerical values. Or as @tohecz pointed out in his comment to another answer:

the unary minus is a "part of the numeral"

In other words, the symbols "-" in "-3" and "-x" are unrelated typographically.

In light of this, I propose this solution. Which is very elegant if you get to the habit of using \num (from siunitx package) around all your numerical literals:

\documentclass{article}
\usepackage{siunitx}
\sisetup{bracket-negative-numbers, open-bracket={
    {}^-% your custom hack here
}, close-bracket={}}

\begin{document}
\noindent
\num{-1}\\
\num{1}\\
\num{-1e3}\\
\num{1e-3}\\
$\num{-3} - \num{4}$\\
$[\num{1}\,\num{-1}\,\num{1}]

\end{document}

Note: I don't particularly advocate for using {}^-, this seems quite extreme. It is just an example to show the difference and I didn't want to clutter the answer with more code. What I advocate is the use of siunitx for fine control over typesetting of numbers.

Besides I wanted to have a code that works also for superscripts (for the exponent) (using hard code raisebox produces weird effects on exponents or small fractions). If know of a short code that can do this elegantly please edit this answer.

Answer 8

I bumped into the same problem when subindexing letters with negative numbers. The "math minus" looks to me too long. Therefore I write a "text minus", i.e., \text{-} before the number. It is quite similar to the solution of @Arne Timperman: his is from text modus, mine from math modus.

\documentclass{article}
\usepackage{amsmath}

\begin{document}
$A_{2\,1\,-1}$ %math minus, a bit excessively long for my taste ;).

$A_{2\,1\,\text{-}1}$ %text minus, in this case looks better.
\end{document}

Answer 9

I've seen it done by simply superscripting the minus sign, i.e. ^- giving e.g.:

\documentclass{article}
\begin{document}
$^-3-4=^-7$
\end{document}

I wouldn't use it routinely, only when it's important to distinguish the two, as when defining negative numbers and how subtraction interacts with them (in arithmatic).

EDIT to my surprise, tex.stackexchange.com doesn't interpret $...$ as latex, unlike e.g. math.stackexchange.com. I guess because it could only support a very limited subset.

EDIT It's good that I tried an actual example, because it renders with extra spacing between the - and 7, but not between the - and 3. I don't know why.