2HOT: An Improved Parallel Hashed Oct-Tree N-Body Algorithm for
  Cosmological Simulation
  We report on improvements made over the past two decades to our adaptive
treecode N-body method (HOT). A mathematical and computational approach to the
cosmological N-body problem is described, with performance and scalability
measured up to 256k ($2^{18}$) processors. We present error analysis and
scientific application results from a series of more than ten 69 billion
($4096^3$) particle cosmological simulations, accounting for $4 \times 10^{20}$
floating point operations. These results include the first simulations using
the new constraints on the standard model of cosmology from the Planck
satellite. Our simulations set a new standard for accuracy and scientific
throughput, while meeting or exceeding the computational efficiency of the
latest generation of hybrid TreePM N-body methods.
