def probability(vr_norm, pmax, cross_sections): # still per cell
    """ Returns the collisions probability associated with the possibly colliding couples.

    Args:
        vr_norm (np.ndarray): array of size (number of candidates) with the relative speed norm for each couple.
                              Can be computed using something like : np.linalg.norm((arr[choices][:,1,2:]-arr[choices][:,0,2:]), axis = 1)
        pmax (float): maximum probability for the current cell
        cross_sections (np.ndarray): array of size (number of candidates) containing the cross sections for each couple. 
                                     Note that a *float* can also be used and it will return the right result. 
                                     It is useful when dealing with constant cross sections accross couples.

    Returns:
        [np.ndarray]: 1D-array of size (number of candidates) containing the probability of collisions for each couple.
    """
    return cross_sections/pmax*vr_norm