# COSMOS: A Hybrid N-Body/Hydrodynamics Code for Cosmological Problems

## Abstract

We describe a new hybrid N-body/hydrodynamical code based on the particle-mesh (PM) method and the piecewise-parabolic method (PPM) for use in solving problems related to the evolution of large-scale structure, galaxy clusters, and individual galaxies. The code, named COSMOS, possesses several new features that distinguish it from other PM-PPM codes. In particular, to solve the Poisson equation we have written a new multigrid solver which can determine the gravitational potential of isolated matter distributions and which properly takes into account the finite-volume discretization required by PPM. All components of the code are constructed to work with a nonuniform mesh, preserving second-order spatial differences. The PPM code uses vacuum boundary conditions for isolated problems, preventing inflows when appropriate. The PM code uses a second-order variable-time-step time integration scheme. Radiative cooling and cosmological expansion terms are included. COSMOS has been implemented for parallel computers using the Parallel Virtual Machine (PVM) library, and it features a modular design which simplifies the addition of new physics and the configuration of the code for different types of problems. We discuss the equations solved by COSMOS and describe the algorithms used, with emphasis on these features. We also discuss the results of tests we have performedmore »

- Authors:

- Publication Date:

- OSTI Identifier:
- 20217584

- Resource Type:
- Journal Article

- Journal Name:
- Astrophysical Journal

- Additional Journal Information:
- Journal Volume: 536; Journal Issue: 1; Other Information: PBD: 10 Jun 2000; Journal ID: ISSN 0004-637X

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COSMOLOGY; MANY-BODY PROBLEM; HYDRODYNAMICS; GALAXY CLUSTERS; COMPUTER CODES; ALGORITHMS; THEORETICAL DATA

### Citation Formats

```
Ricker, P. M., Dodelson, S., and Lamb, D. Q.
```*COSMOS: A Hybrid N-Body/Hydrodynamics Code for Cosmological Problems*. United States: N. p., 2000.
Web. doi:10.1086/308908.

```
Ricker, P. M., Dodelson, S., & Lamb, D. Q.
```*COSMOS: A Hybrid N-Body/Hydrodynamics Code for Cosmological Problems*. United States. doi:10.1086/308908.

```
Ricker, P. M., Dodelson, S., and Lamb, D. Q. Sat .
"COSMOS: A Hybrid N-Body/Hydrodynamics Code for Cosmological Problems". United States. doi:10.1086/308908.
```

```
@article{osti_20217584,
```

title = {COSMOS: A Hybrid N-Body/Hydrodynamics Code for Cosmological Problems},

author = {Ricker, P. M. and Dodelson, S. and Lamb, D. Q.},

abstractNote = {We describe a new hybrid N-body/hydrodynamical code based on the particle-mesh (PM) method and the piecewise-parabolic method (PPM) for use in solving problems related to the evolution of large-scale structure, galaxy clusters, and individual galaxies. The code, named COSMOS, possesses several new features that distinguish it from other PM-PPM codes. In particular, to solve the Poisson equation we have written a new multigrid solver which can determine the gravitational potential of isolated matter distributions and which properly takes into account the finite-volume discretization required by PPM. All components of the code are constructed to work with a nonuniform mesh, preserving second-order spatial differences. The PPM code uses vacuum boundary conditions for isolated problems, preventing inflows when appropriate. The PM code uses a second-order variable-time-step time integration scheme. Radiative cooling and cosmological expansion terms are included. COSMOS has been implemented for parallel computers using the Parallel Virtual Machine (PVM) library, and it features a modular design which simplifies the addition of new physics and the configuration of the code for different types of problems. We discuss the equations solved by COSMOS and describe the algorithms used, with emphasis on these features. We also discuss the results of tests we have performed to establish that COSMOS works and to determine its range of validity. (c) 2000 The American Astronomical Society.},

doi = {10.1086/308908},

journal = {Astrophysical Journal},

issn = {0004-637X},

number = 1,

volume = 536,

place = {United States},

year = {2000},

month = {6}

}