<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _combine_msd_quan(msd, quan):
 """Combine msd and quantiles in chain summary Parameters msd : array of shape (num_params, 2, num_chains) mean and sd for chains cquan : array of shape (num_params, num_quan, num_chains) quantiles for chains Returns ------- msdquan : array of shape (num_params, 2 + num_quan, num_chains) """

    dim1 = msd.shape
    n_par, _, n_chains = dim1
    ll = []
    for i in range(n_chains):
        a1 = msd[:, :, i]
        a2 = quan[:, :, i]
        ll.append(np.column_stack([a1, a2]))
    msdquan = np.dstack(ll)
    return msdquan