Geodesic Won't Plot

edit

 %display latex 
 M = Manifold(3, 'M', structure='Lorentzian') 
 X.<t,x,y> = M.chart('t x y') 
 X 
 v=.5
 r=sqrt((x-v*t)^2+y^2)
 f=(tanh(r+4)-tanh(r-4))/(2*tanh(4)) 
 g = M.metric() 
 g[0,0] = (v^2*f^2-1) 
 g[0,1] = -v*f 
 g[1,1] = 1 
 g[2,2] = 1
 g.display() 
 p = M((0,0,1), name='p')
 v = M.tangent_space(p)((2/3,1,0), name='v') 
 v.display() 
 s = var('s') 
 c = M.integrated_geodesic(g, (s, 0, 10), v, name='c') 
 sol = c.solve() 
 interp = c.interpolate() 
 graph = c.plot_integrated() 
 p_plot = p.plot(size=30, label_offset=-0.07,
 fontsize=20) v_plot =
 v.plot(label_offset=0.05, fontsize=20)
 graph + p_plot + v_plot

This either doesn't work or takes an indeterminate amount of time to plot. However, if I change v from 0.5 to 1, it does fine. Any idea why that is?