30 setxunit
20 setborder
90 setangle_repere
-5 5 setxrange
-5 5 setyrange
1 1 settkstep
.5 .5 setsubtkstep
2 2 setmkstep
ticks
subticks
marks
traceaxes
axesarrow
/R {settvar
    4 120 t 3 exp div sub
} def
  2.5  8 pi mul settrange
gsave
   .75 setcurvelinewidth
   continu
   noir
   (R) courbepolar
grestore