\def{text f=\parm1}
\def{text g=\parm2}
\def{integer pas=\parm3}
\def{real centrex=\parm4}
\def{real centrey=\parm5}
\def{real xy_size= \parm6}
\def{real taille= \parm7}
\def{text data=}
\for{ a=-\pas to \pas}{
\def{real u= \centrex+((\a)*\xy_size/\pas)}
 \for{b=-\pas to \pas}
	 { 
	 \def{real v=\centrey+((\b)*\xy_size/\pas)}
	\def{real  A= evalue(\f,x=\u,y=\v)}
	\def{real B= evalue(\g,x=\u,y=\v)}
	\def{real N=((\A)^2+(\B)^2)^(1/2)}
	\if{\N>10^(-2)}{
	\def{text data=\data
	arrow \u,\v,\u+(\A/(\N)),\v+(\B/(\N)), 5,green}
	}}}
\draw{\taille,\taille}
{xrange \centrex-\xy_size, \centrex+\xy_size
yrange \centrey-\xy_size, \centrey+\xy_size
parallel \centrex-\xy_size,\centrey-\xy_size,\centrex+\xy_size,\centrey-\xy_size,0,\xy_size/10,20,grey
parallel \centrex-\xy_size,\centrey-\xy_size,\centrex-\xy_size,\centrey+\xy_size,\xy_size/10,0,20,grey
arrow 0,0, 0,1,10,black
arrow 0,0, 1, 0 ,10,black
vline 0,0, black
hline 0,0, black
\data
}
