Using Greek letter qoppa in a formula [duplicate]

I'd like to use the Greek letter qoppa in a formula in an otherwise non-Greek document. I tried using the greekoption for babelbut that turned my document into Greek letters. By default, \qoppadoesn't seem to be defined.

marked as duplicate by Malipivo, Svend Tveskæg, user13907, Andrew, ThorstenApr 5 '15 at 11:59

Since the qoppa is a stylized symbol, there's probably no need to try and find a version suitable for any font.

Since you want it in math, the simplest thing is to define a stripped down version of the LGR encoding.

\documentclass{article}
\usepackage{amsmath,pdftexcmds}

\DeclareFontFamily{U}{cbgreek}{}
\DeclareFontShape{U}{cbgreek}{m}{n}{
<-6>    grmn0500
<6-7>   grmn0600
<7-8>   grmn0700
<8-9>   grmn0800
<9-10>  grmn0900
<10-12> grmn1000
<12-17> grmn1200
<17->   grmn1728
}{}
\DeclareFontShape{U}{cbgreek}{bx}{n}{
<-6>    grxn0500
<6-7>   grxn0600
<7-8>   grxn0700
<8-9>   grxn0800
<9-10>  grxn0900
<10-12> grxn1000
<12-17> grxn1200
<17->   grxn1728
}{}

\DeclareRobustCommand{\qoppa}{%
\text{\usefont{U}{cbgreek}{\normalorbold}{n}\symbol{19}}%
}
\DeclareRobustCommand{\Qoppa}{%
\text{\usefont{U}{cbgreek}{\normalorbold}{n}\symbol{21}}%
}
\makeatletter
\newcommand{\normalorbold}{%
\ifnum\pdf@strcmp{\math@version}{bold}=\z@ bx\else m\fi
}
\makeatother

\begin{document}

$\qoppa+\xi=\alpha-\Qoppa$

\boldmath

$\qoppa+\xi=\alpha-\Qoppa$

\end{document}