# double sqrt (surd) symbol

I want to define a macro that prints two adjacent sqrt symbols. (Notation from Cauchy's analysis book).

I get something close but the spacing is changing depending if there is a number before it. If there is not a number in front the sqrt (surd) symbols are too close.

MWE

\documentclass[class=book]{book}
% Run with xelatex

%%% fonts
\usepackage{libertine}

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}

%%% mathfonts
\usepackage{unicode-math}
\setmathfont{texgyrepagella-math.otf}
\usepackage{microtype}

% "221A is the surd symbol in unicode. \surd is not working, it shows a p
\usepackage{mathtools}
\NewDocumentCommand\dsqrt{o m}{%
\IfNoValueTF{#1}{%
\,\mathrlap{\char"221A}\,\char"221A#2%
}%
{
\,\mathrlap{\raisebox{3pt}{$\scriptscriptstyle#1$}}\mathrlap{\char"221A}\,\char"221A#2%
}
}

\begin{document}

$$\label{pre1} \dsqrt{a} = \pm\sqrt{a}$$

$$\label{pre1} 2\dsqrt{a} = \pm2\sqrt{a}$$

$$\label{pre1} \dsqrt[n]{a} = \pm\sqrt[n]{a}$$

$$\label{pre1} 2\dsqrt[n]{a} = \pm2\sqrt[n]{a}$$

And here is another: inline  $\dsqrt{y} =\pm \sqrt{y}$.

And here is another: inline  $2\dsqrt{y} =\pm 2\sqrt{y}$.

And here is another: inline $\dsqrt[n]{y} =\pm \sqrt[n]{y}$.

And here is another: inline $2\dsqrt[n]{y} =\pm 2\sqrt[n]{y}$.

\end{document}


• Obviously I'm no Cauchy but his notation is ugly as hell. – percusse Jan 13 '16 at 12:34
• At the moment in the old book looks nicer, but I don't like either. I am working in a translation – TeXtnik Jan 13 '16 at 12:36
• @TeXtnik Can you post an image of the original? – egreg Jan 13 '16 at 12:40
• You can see an example here (dl.dropboxusercontent.com/u/196902/Cauchy.pdf) – TeXtnik Jan 13 '16 at 14:02
• @TeXtnik -- can you please provide the full bibliographic information on the book? (i've forwarded information regarding this inquiry to my unicode contacts.) – barbara beeton Jan 13 '16 at 15:33

Here's another attempt; unfortunately, it seems that the “surd” symbol is not available in Unicode.

\documentclass{book}
% Run with xelatex

%%% fonts
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{amsfonts}
\usepackage{amssymb}

%%% mathfonts
\usepackage{unicode-math}
\setmainfont{TeX Gyre Pagella}
\setmathfont{texgyrepagella-math.otf}
\usepackage{microtype}

% "221A is the surd symbol in unicode. \surd is not working, it shows a p
\NewDocumentCommand\dsqrt{o m}{%
\mathop{%
\IfNoValueTF{#1}
{\doublesurd}
{\mathrlap{^{\scriptscriptstyle#1}}\doublesurd}%
}%
{}#2
}

\makeatletter
\newcommand{\doublesurd}{\mathpalette\double@surd\relax}
\newcommand{\double@surd}[2]{%
\ooalign{$\m@th#1\char"221A$\hidewidth\cr$\m@th#1\,\char"221A$\cr}%
}
\makeatother

\begin{document}

$$\dsqrt{a} = \pm\sqrt{a}$$

$$2\dsqrt{a} = \pm2\sqrt{a}$$

$$\dsqrt[n]{a} = \pm\sqrt[n]{a}$$

$$2\dsqrt[n]{a} = \pm2\sqrt[n]{a}$$

And here is another: inline  $\dsqrt{y} =\pm \sqrt{y}$.

And here is another: inline  $2\dsqrt{y} =\pm 2\sqrt{y}$.

And here is another: inline $\dsqrt[n]{y} =\pm \sqrt[n]{y}$.

And here is another: inline $2\dsqrt[n]{y} =\pm 2\sqrt[n]{y}$.

\end{document}


• I choose this one, because I think it gives better result at different math style. – TeXtnik Jan 15 '16 at 8:13

Here is a version that uses stacks. It is not currently set up to obey the smaller math styles, however.

\documentclass[class=book]{book}
% Run with xelatex

%%% fonts
\usepackage{libertine}

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{stackengine}
\stackMath
%%% mathfonts
\usepackage{unicode-math}
\setmathfont{texgyrepagella-math.otf}
\usepackage{microtype}

% "221A is the surd symbol in unicode. \surd is not working, it shows a p
\usepackage{mathtools}
\NewDocumentCommand\dsqrt{o m}{%
\IfNoValueTF{#1}{%
\,\stackengine{0pt}{\char"221A}{\,\char"221A#2}{O}{l}{F}{F}{L}%
}%
{
\,\raisebox{3pt}{$\scriptscriptstyle#1$}\mkern-13mu\stackengine{0pt}{\char"221A}{\,\char"221A#2}{O}{l}{F}{F}{L}%
}
}

\begin{document}

$$\label{pre1} \dsqrt{a} = \pm\sqrt{a}$$

$$\label{pre1} 2\dsqrt{a} = \pm2\sqrt{a}$$

$$\label{pre1} \dsqrt[n]{a} = \pm\sqrt[n]{a}$$

$$\label{pre1} 2\dsqrt[n]{a} = \pm2\sqrt[n]{a}$$

And here is another: inline  $\dsqrt{y} =\pm \sqrt{y}$.

And here is another: inline  $2\dsqrt{y} =\pm 2\sqrt{y}$.

And here is another: inline $\dsqrt[n]{y} =\pm \sqrt[n]{y}$.

And here is another: inline $2\dsqrt[n]{y} =\pm 2\sqrt[n]{y}$.

\end{document}


If one wanted the surd to match the argument size (as occurs with the \sqrt), then this definition should be substituted:

\NewDocumentCommand\dsqrt{o m}{%
\IfNoValueTF{#1}{%
\,\stackengine{0pt}{\sqrt{\vphantom{#2}}}{\,\sqrt{#2}}{O}{l}{F}{F}{L}%
}%
{
\,\raisebox{3pt}{$\scriptscriptstyle#1$}\mkern-13mu\stackengine{0pt}{%
\sqrt{\vphantom{#2}}}{\,\sqrt{#2}}{O}{l}{F}{F}{L}%
}
}


Notice the difference with an x vs. a y argument.