square root of number in counter

Question

I would like to get the square root of a number which I have stored into a counter. I have been using the calc package for summation and multiplication operations, but I cannot find anything like

\setcounter{squarerootofmynumber}{\value{mynumber}^{1/2}}

or something like that. Do you know the way?

Answer 1

Here are four ways for calculating the square root of a number (with varying precision). However, the result cannot be stored in a counter unless it is an integer.

1. The calculator package

   \documentclass{article}
   \usepackage{calculator}
   \newcounter{mycount}
   \setcounter{mycount}{7}
   \begin{document}
   \SQUAREROOT{\themycount}{\solution}%
   $\sqrt{\themycount}=\solution$
   \end{document}
   

2. The fp package

   \documentclass{article}
   \usepackage{fp}
   \newcounter{mycount}
   \setcounter{mycount}{7}
   \begin{document}
   \FProot\solution{\themycount}{2}%
   \FPround\solution\solution{5}%
   $\sqrt{\themycount}=\solution$
   \end{document}
   

3. The pgf package (thanks to Peter Grill for the reminder)

   \documentclass{article}
   \usepackage{pgf}
   \newcounter{mycount}
   \setcounter{mycount}{7}
   \begin{document}
   \pgfmathsetmacro{\solution}{sqrt(\themycount)}%
   $\sqrt{\themycount}=\solution$
   \end{document}
   

4. The l3fp module of the l3kernel

   \documentclass{article}
   \usepackage{expl3}
   \ExplSyntaxOn
   \cs_new_eq:NN \calculate \fp_eval:n
   \ExplSyntaxOff
   \newcounter{mycount}
   \setcounter{mycount}{7}
   \begin{document}
   $\sqrt{\themycount}=\calculate{round(\themycount^(1/2),5)}$
   \end{document}
   

All of these examples give

Storing the result in a counter requires the result to be an integer. Packages 2-4 have means to round a result which would allow to set a counter afterwards. Here is an example with l3fp:

\documentclass{article}
\usepackage{expl3}
\ExplSyntaxOn
\cs_new_eq:NN \calculate \fp_eval:n
\ExplSyntaxOff
\begin{document}
\newcounter{mycount}
\setcounter{mycount}{7}
\edef\solution{\calculate{round(\value{mycount}^(1/2),0)}}
\setcounter{mycount}{\solution}\themycount
\end{document}

Answer 2

a solution with lualatex with a good precision

\documentclass{minimal}
\newcounter{mycount} \setcounter{mycount}{7}
\begin{document}

\directlua{tex.print(math.sqrt(\themycount))}

\end{document}