f1(u,v) = (exp(b*v)+ exp(a*v)*cos(u))*cos(v)
f2(u,v) = (exp(b*v)+ exp(a*v)*cos(u))*sin(v)
f3(u,v) = exp(a*v)*sin(u)

set parametric
set samples 18
set isosamples 36
set ur [0:2*pi]
set vr [0:pi]
set zr [0:160]
set yr [-60:60]
set xyplane 0        # 'set ticslevel 0' is obsolute
unset key
set pm3d hidden3d 100 depthorder
set style line 100 lt -1 lw 0.2
set palette defined (0 "dark-red", 1 "yellow") 
set title 'cornucopia (pm3d)' font "Times,20" 
set term pngcairo enh font ",8" size 480,360
set out "3dparam_cornucopia.png"
a = 1
b = 1.5
splot f1(u,v), f3(u,v), 3*f2(u,v) w pm3d