# Self Gravity: XSEDE report

In order to test the self-gravity implementation in CHOLLA, I ran a adiabatic simulation of an ideal gas collapsing under it’s own gravity.

The box size is , the density in the box is and for the spherical region of there is an over-density of . Initial velocities are uniform and pressure is uniform .

The next figures show density and potential center slices. The black circle corresponds to the analytical value for the radius of a uniform pressure-less system collapsing only under gravity.

**Density**

**Potential**

## Timing for several grid configurations

All times are in seconds and correspond to the average of the first 20 time-steps ( not counting the first two time-steps )

nGPUs | nx | ny | nz | time_hydro | time_potential | time_boundaries |
---|---|---|---|---|---|---|

8 | 256 | 256 | 256 | 0.613 | 0.689 | 0.275 |

16 | 512 | 256 | 256 | 0.691 | 0.762 | 0.339 |

32 | 512 | 512 | 256 | 0.818 | 1.513 | 0.939 |

64 | 512 | 512 | 512 | 0.869 | 1.972 | 1.361 |

128 | 1024 | 512 | 512 | 0.932 | 2.121 | 1.592 |

For the XSTREAM system there was no debug queue, this makes any development to be very tedious, and I wasn’t able to run more than 128 GPUs.

NOTE: This was the implementation of the poisson solver that wasn’t optimized for solving real-complex-real FFTs, also there was another optimization that avoided the last transposition for the forward FFT saving communication time.