p = 30
e(x) = 10.0**((log10(x)*20-p)/10)
f(x) = (x-e(x) < 0)?0:(x-e(x))
d(x,y) = abs(x-f(y))

set ticslevel 0
set contour
set cntrparam bspline
set cntrparam points 10
set cntrparam order 10
set cntrparam levels incremental 0,5,100
set nosurface
set term table
set out 'data.out'
splot [1:1000] [1:1000] d(x,y)
set out
set term X11
set data style lines
plot 'data.out' index 0 t "100", \
        'data.out' index 3 notitle, \
        'data.out' index 6 t "70", \
        'data.out' index 9 notitle, \
        'data.out' index 12 t "60", \
        'data.out' index 15 notitle, \
        'data.out' index 18 t "10"