25 setxunit
7.5 setborder
-5 5 setxrange
-5 5 setyrange
jpegmode
/a 4 def
/k 7 def

1 1 settkstep
.5 .5 setsubtkstep
2 2 setmkstep
ticks
subticks
marks
traceaxes
axesarrow
/R {settvar
    a k t mul Sin mul
} def
  0  2 pi mul settrange
gsave
   .75 setlinewidth
   continu
   bleu
   (R) courbepolar
grestore