Error with gnuplot and babel greek

Question

In my preample i use the babel to load the greek language along with the txfontsb package for greek letters. In order to create a plot using gnuplot, i use the following code : -synctex=1 -interaction=nonstopmode -enable-write18 next to my pdflatex command.

\documentclass[a4paper,11pt]{article}
\usepackage{pgfplots}
\usepackage{tkz-fct}
\usepackage{psfrag}
\usepackage[english,greek]{babel}
\usepackage[iso-8859-7]{inputenc}
\usepackage{amsmath}
\usepackage[T1]{fontenc}
 \usepackage{txfontsb}
\begin{document}
%Γράφημα
\begin{tikzpicture}[scale=1.25]
\tkzInit[xmin=-5,xmax=5,ymax=2]
\tkzGrid
\tkzAxeXY
\tkzFct[color=red]{2*x**2/(x**2+1)}
\end{tikzpicture}
\end{document}

When i disable the \usepackage[english,greek]{babel} command using % everything works fine. But when i use it i get the folloing errors :

Missing \endcsname inserted \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \fi \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \fi \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \fi \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \fi \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \endcsname \tkzFct[color=red]{2*x**2/(x**2+1)}
Missing \endcsname inserted \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \fi \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \fi \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \fi \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \endcsname \tkzFct[color=red]{2*x**2/(x**2+1)}
Missing $ inserted \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra }, or forgotten $ \tkzFct[color=red]{2*x**2/(x**2+1)}
Extra \fi \tkzFct[color=red]{2*x**2/(x**2+1)}
Missing $ inserted \end{tikzpicture}
Missing } inserted \end{tikzpicture}
running in backwards compatibility mode (unsuitable tick labels; missing features). Consider writing \pgfplotsset{compat=1.11} into your preamble.
Overfull \hbox (41.38289pt too wide) in paragraph

How can i make them work together?

Answer 1

The tkz-fct package uses \alph for making internal labels, but this fails when babel-greek is loaded, because \alph (actually the internal version \@alph) is redefined to produce Greek letters.

This should be considered a bug in tkz-fct, but there is a workaround, albeit a bit ugly.

\documentclass[a4paper,11pt]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\makeatletter
% save a copy of the original \@alph command
\let\latex@alph\@alph
% a command to (locally) restore the original \@alph command
\newcommand{\safealph}{\let\@alph\latex@alph}
\makeatother

\usepackage[english,greek]{babel}

\usepackage{pgfplots}
\usepackage{tkz-fct}
\usepackage{amsmath}

\begin{document}
%Γράφημα
\begin{tikzpicture}[scale=1.25]
\safealph
\tkzInit[xmin=-5,xmax=5,ymax=2]
\tkzGrid
\tkzAxeXY
\tkzFct[color=red]{2*x**2/(x**2+1)}
\end{tikzpicture}
\end{document}