Calculate B matrix for multiple theta and specific components
Calculate B matrix for multiple theta and specific components

Calculate B matrix for multiple theta such that B*d gives a
1-dimensional array of the selected components [0=u,1=v,1=w,3=phi]
repeated for each value of theta.

Example: Get the lateral displacement at each spoke:
  u_s = rr.B_theta(theta_s, 0)

Example: Get the radial and tangential displacement at theta = pi
  vw = rr.B_theta(np.pi, [1, 2])

dashdotrobot/bike-wheel-calc