  The halo occupation distribution (HOD) approach has proven to be an effective
method for modeling galaxy clustering and bias. In this approach, galaxies of a
given type are probabilistically assigned to individual halos in N-body
simulations. In this paper, we present a fast emulator for predicting the fully
nonlinear galaxy power spectrum over a range of freely specifiable HOD modeling
parameters. The emulator is constructed using results from 100 HOD models run
on a large LCDM N-body simulation, with Gaussian Process interpolation applied
to a PCA-based representation of the galaxy power spectrum. The total error is
currently ~3% (~2% in the simulation and ~1% in the emulation process) from z=1
to z=0, over the considered parameter range. We use the emulator to investigate
parametric dependencies in the HOD model, as well as the behavior of galaxy
bias as a function of HOD parameters. The emulator is publicly available at
http://www.hep.anl.gov/cosmology/CosmicEmu/emu.html.
