= Fast Simulations of Gravitational Many-body Problem on RV770 GPU =
== abstract ==
The gravitational many-body problem is a problem concerning the movement of bodies, which are interacting through gravity. However, solving the gravitational many-body problem with a CPU takes a lot of time due to O(N^2^) computational complexity. 
In this paper, we report our technique to speed-up the exact force-calculation on RV770 GPU from AMD/ATi.
As far as we know, our implementation on RV770 GPU running at 750 MHz shows fastest
performance of ~ 1 Tflops thanks to efficient cache architecture of RV770 GPU. 
This is accomplished by a simple loop-unrolling technique that is highly effective RV770 GPU.

== Result ==
[[Image(bare.png)]] 

== preprint ==
http://jp.arxiv.org/abs/0904.3659


= Oct-tree Method on GPU: $42/Gflops Cosmological Simulation =
== abstract ==
The kd-tree is a fundamental tool in computer science.
Among others, an application of the kd-tree search
(oct-tree method) to fast evaluation of particle interactions
and neighbor search is highly important
since computational complexity of these problems
are reduced from O(N^2^) with a brute force method
to O(N log N) with the tree method where N is a number of particles.
In this paper, we present a parallel implementation of
the tree method running on a graphic processor unit (GPU).
We successfully run a simulation of structure formation
in the universe very efficiently.
On our system, which costs roughly $900,
the run with N ~ 2.87 x 10^6^ particles
took 5.79 hours and executed 1.2 x 10^13^ force evaluations in total.
We obtained the sustained computing speed of 21.8 Gflops
and the cost per Gflops of $41.6/Gflops that is two and half times better than 
the previous record in 2006.

== Result == 
[[Image(time.png)]] 

== preprint == 
to be posted


= Demo programs =
to be posted