Upper and lower bounds for some depth-3 circuit classes

We investigate the complexity of depth-3 threshold circuits with majority gates at the output, possibly negated AND gates at level two, and MODm gates at level one. We show that the fan-in of the AND gates can be reduced toO(logn) in the case wherem is unbounded, and to a constant in the case wherem is constant. We then use these upper bounds to derive exponential lower bounds for this class of circuits. In the unboundedm case, this yields a new proof of a lower bound of Grolmusz; in the constantm case, our result sharpens his lower bound. In addition, we prove an exponential lower bound if OR gates are also permitted on level two andm is a constant prime power.

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