%!

/a [ 1 0 ] def
/b [ 0.5 3 sqrt 2 div ] def

/N 20 def

/S 72 def
S dup scale
1 S div setlinewidth

4 4 translate

newpath
N neg 1 N { /i exch def
  N neg 1 N { /j exch def
    a 0 get i mul b 0 get j mul add
    a 1 get i mul b 1 get j mul add
    2 copy moveto
    % without the moveto, arc adds in a line from one disk to another
    0.1 0 360 arc
  } for
} for
fill