# set terminal pngcairo  background "#ffffff" enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'pm3d.9.png'
set border 4095 front linetype -1 linewidth 1.000
set view map
set samples 50, 50
set isosamples 50, 50
unset surface 
set style data pm3d
set style function pm3d
set ticslevel 0
set title "colour, rgbformulae 3,11,6 ... green-red-violet" 
set xlabel "x" 
set xrange [ -15.0000 : 15.0000 ] noreverse nowriteback
set ylabel "y" 
set yrange [ -15.0000 : 15.0000 ] noreverse nowriteback
set zrange [ -0.250000 : 1.00000 ] noreverse nowriteback
set pm3d implicit at b
set palette rgbformulae 3, 11, 6
splot sin(sqrt(x**2+y**2))/sqrt(x**2+y**2)