25 setxunit
7.5 setborder
90 setangle_repere
-3.1 3.1 setxrange
-3.1 3.1 setyrange
1 setquadrillagexstep
1 setquadrillageystep
quadrillage
1 1 settkstep
.5 .5 setsubtkstep
1 1 setmkstep
ticks
ysubticks
marks
traceaxes
axesarrow
/R {settvar
#rpn#   1+2*Cos(3*t)
} def
  0  6 pi mul 3 div settrange
gsave
   0.75 setlinewidth
   continu
   noir
   (R) courbepolar
grestore