from mpl_toolkits.mplot3d import Axes3D

costPath = np.array([np.log(((X.dot(wtmp)-y)**2).sum()) for wtmp in allw])
costOpt  = np.log(((X.dot(wstar)-y)**2).sum())

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
ax.plot_surface(w1, w2, cost, rstride = 1, cstride=1 )
ax.scatter(wstar[0], wstar[1],costOpt, c='r')
ax.plot(allw[:,0],allw[:,1],costPath, 'b+-' ,lw=2 )