-5 5 setxrange
-7 5 setyrange
-5 5 setyrange
30 setxunit

gsave
masque
quadrillage

/f {
2 dict begin
   /y exch def
   /x exch def
%%   x -2 x mul y mul add
#rpn# x - 2*x*y
end
} def

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

{f} .25 .25 .1 champvecteur

/arrowscale {.75 dup} def
.7 setlinewidth
noir
tracerepere

1 setlinewidth

%% on represente quelques solutions
-3 1 7 {
   /i exch def
   bleu
   [{f} 1 i 4 div .1 euler] ligne
} for

grestore

#tex# $y' + 2xy = x$
0 -6 [2 dup] cctexlabel