ruby
def omega(t)
  if t > 10
    return 3 - 0.2*(t - 10)
  else
    return 1 + 0.2 * t
  end
end
ruby end

xr = -1:21

math /xrange 0:20 /samples=1000
setup-grid 1x1,2 /top=1mm /right=2mm /dy=2mm
inset grid:0,0
  plot 'omega(x)'
  ylabel '$\omega(t)$'
  no-xlabel
  bottom ticks
  margin 0.08
  xrange $(xr)
next-inset grid:0,1
  plot 'sin(omega(x) * x)'
  ylabel '$\sin \left\{\omega(t) \, t\right\}$'
  xlabel '$t$'
  margin 0.03
  xrange $(xr)
end