  We have applied an eccentric accretion disc theory in simplified form to the
case of an accretion disc in a binary system, where the disc contains the 3:1
Lindblad resonance. This is relevant to the case of superhumps in SU Ursae
Majoris cataclysmic variables and other systems, where it is thought that this
resonance leads to growth of eccentricity and a modulation in the light curve
due to the interaction of a precessing eccentric disc with tidal stresses. A
single differential equation is formulated which describes the propagation,
resonant excitation and viscous damping of eccentricity. The theory is first
worked out in the simple case of a narrow ring and leads to the conclusion that
the eccentricity distribution is locally suppressed by the presence of the
resonance, creating a dip in the eccentricity at the resonant radius.
Application of this theory to the superhump case confirms this conclusion and
produces a more accurate expression for the precession rate of the disc than
has been previously accomplished with simple dynamical estimates.
