-4 4 setxrange
-3 3 setyrange
40 setxunit

gsave
masque


/f {
2 dict begin
   /x exch def
   /y exch def
#rpn# 1/(1+y*y)
end
} def

.5 setlinewidth
/arrowscale {.5 dup} def
.4 setgray

{f} .5 .5 .3 (->) champvecteur

/arrowscale {.75 dup} def
.7 setlinewidth
noir
traceaxes
axesarrow

%% on represente quelques solutions
-3 0.5 3 {
   /i exch def
   bleu
   [xmin xmax {f} 0 i .1 Euler] ligne
   } for