100 setxunit
7.5 setborder
90 setangle_repere
-2 3.1 setxrange
-3 3 setyrange
1 1 settkstep
.5 .5 setsubtkstep
0.5 0.5 setmkstep
ticks
subticks
marks
traceaxes
axesarrow
/R {settvar
#rpn#   Cos(3*t)-2
} def
 0 2 pi mul  settrange
gsave
   .75 setlinewidth
   continu
   bleu
   (R) courbepolar
grestore