[pgfplots] Не работает addplot (gnuplot | function)

nikita@nikita-notebook ~/education/tex $ xelatex -shell-escape pgfplots.tex 
This is XeTeX, Version 3.1415926-2.2-0.9995.2 (Web2C 2009)
 \write18 enabled.
entering extended mode
(./pgfplots.tex
LaTeX2e <2009/09/24>
Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh
yphenation, bulgarian, russian, ukrainian, loaded.

...

! Undefined control sequence.
\pgf@gnuplot@head ...le \pgf@plottablefile@quoted 
                                                  ; set format "%.5f"
l.10 ...plot plot[id=a] function {(-0.5 * x - 2)};
                                                  
? 

set table ; set format "%.5f"{pgfplots.a}
                             ^
"pgfplots.a.gnuplot", line 1: invalid complex constant


! Package pgfplots Error: Sorry, the gnuplot-result file 'pgfplots.a.table' cou
ld not be found. Maybe you need to enable the shell-escape feature? For pdflate
x, this is '>> pdflatex -shell-escape'. You can also invoke '>> gnuplot <file>.
gnuplot' manually on the respective gnuplot file..

See the pgfplots package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.10 ...plot plot[id=a] function {(-0.5 * x - 2)};
                                                  
? 

! LaTeX Error: Can be used only in preamble.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.13 \begin{document}
                     
? x
No pages of output.
Transcript written on pgfplots.log.

\documentclass{minimal}
\usepackage{tikz,pgfplots}

\pgfplotsset{compat=default}

\begin{document}
\begin{tikzpicture}
  \begin{axis}[xmin=-3, xmax=5, ymin=-4, ymax=5]
    \addplot plot[id=a] function {(-0.5 * x - 2)};
  \end{axis}
\end{tikzpicture}
\begin{document}