It is suggested that observed variations in the luminosity function from one cluster to another, as well as from the inner to outer regions of the same cluster, are produced by the dynamical friction force acting on galaxies as they move through the cluster. Dynamical friction makes galaxies lose their energy, sink from outer regions to inner ones, and eventually be "swallowed" by the center. The force depends on the galaxy's energy and angular momentum as well as on its mass, thus making decay of galactic orbits non-self-similar in mass, leading to a change in the shape of luminosity function.
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A. Kashlinsky (1987) studied this question.