pro circle_draw,np,x,y

;  make a set of X & Y points that will form a circle (i.e., plot,x,y), 
;  for the input NP # of points, the range in X & y is -1 to 1

   np2 = np/2.
   
   x = (findgen(np+1) - np2) / np2   
   
   y = sqrt(1^2 - x^2)
      
   x = [x,reverse(   x)]  
   y = [y,reverse(-1*y)]
      
;- done

   return
   end