# set terminal pngcairo  background "#ffffff" enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'hidden.2.png'
set samples 20, 20
set isosamples 20, 20
set hidden3d back offset 1 trianglepattern 3 undefined 1 altdiagonal bentover
set style data lines
set title "Hidden line removal of explicit surfaces" 
set xrange [ -1.00000 : 1.00000 ] noreverse nowriteback
set yrange [ -1.00000 : 1.00000 ] noreverse nowriteback
splot x*y / (x**2 + y**2 + 0.1)