def weight_function(run_params, displacement_norm):
    """Determine motion-dependent prediction weight of given supporter point.

    This method determines the weight to apply to each supporter point when
    using it for prediction of a target point based on the norm of its
    displacement vector. The larger the displacement, the higher weight the
    supporter point receives; the weight is a linear function of the
    displacement norm, with an offset of 1.

    Displacement-based weighting is used to give less importance to supporter
    points that are part of the "background" and have little correlation with
    the movement of the muscle fascia.

    Args:
        run_params (ParamValues): values of parameters used in tracking,
            including scalar alpha
        displacement_norm (float): L2 norm of relevant supporter point's
            displacement vector

    Returns:
        float weighting applied to supporter point when tracking target point
    """
    alpha = run_params.displacement_weight

    return 1 + (alpha * displacement_norm)