set parametric
set trange [-2*pi/3:2*pi]
set size ratio -1
set samples 400
unset border
set xtics axis
set ytics axis 1
set xzeroaxis lt -1
set yzeroaxis lt -1
unset key
f(a,t) = t - a*sin(t)
g(a,t) = 1 - a*cos(t)
set title "trochoid" font "Times,20"
set term pngcairo enh font "Times,8" size 480,360
set out "2dparam_trochoid.png"
set object circle center 0,1 radius 1 fs solid 1 fc rgb "gray90" behind
plot \
f(2,t),g(2,t), f(1,t),g(1,t), \
f(1/2.0,t),g(1/2.0,t), f(1/3.0,t),g(1/3.0,t)