VINE --用粒子模拟天体物理系统的数值代码I：物理和数值方法的描述
VINE -- A numerical code for simulating astrophysical systems using particles I: Description of the physics and the numerical methods
摘要：
我们提出了一个Fortran 95代码模拟天体物理系统的演变，用粒子来代表底层的流体流动。代码被设计成通用的、灵活的和可扩展的，具有可以在编译时或运行时选择的模块化选项。我们包括一些通用模块，描述了天体物理界通常需要的各种物理过程。该代码可以用作N体代码，使用Leapfrog或Runge-Kutta-Fehlberg积分器在二维或三维中演化一组粒子，每个粒子有或没有单独的时间步长。粒子可以作为$N$体粒子在重力作用下相互作用，并且所有或任何子集也可以使用平滑粒子流体动力学（SPH）方法在流体动力学上相互作用。也可以包括可能在SPH或$N$体粒子附近吸积的大质量点粒子（“恒星”）。默认的自由边界条件可以由模块替换，以包括周期性边界。宇宙膨胀也可能包括在内。也可以选择具有专用“GRAPE”硬件的接口。如果可用，则从GRAPE协处理器获得的力可以透明地替代从基于默认树的计算获得的力。该代码可以在单处理器上不加修改地运行，也可以在大规模共享内存并行机上使用OpenMP编译器指令并行运行。与Springel 2005的Gadget-2代码相比，在SGI Altix上运行8个Itanium~2处理器时，VINE的引力计算速度快$\approx 3.5 - 4.8$倍，而在我们的测试问题中产生几乎相同的结果。我们提出了几个测试问题的模拟，包括合并模拟两个椭圆星系与80万粒子。
英文摘要：
We present a Fortran 95 code for simulating the evolution of astrophysical systems using particles to represent the underlying fluid flow. The code is designed to be versatile, flexible and extensible, with modular options that can be selected either at compile time or at run time. We include a number of general purpose modules describing a variety of physical processes commonly required in the astrophysical community. The code can be used as an N-body code to evolve a set of particles in two or three dimensions using either a Leapfrog or Runge-Kutta-Fehlberg integrator, with or without individual timesteps for each particle. Particles may interact gravitationally as $N$-body particles, and all or any subset may also interact hydrodynamically, using the Smoothed Particle Hydrodynamic (SPH) method. Massive point particles (`stars') which may accrete nearby SPH or $N$-body particles may also be included. The default free boundary conditions can be replaced by a module to include periodic boundaries. Cosmological expansion may also be included. An interface with special purpose `GRAPE' hardware may also be selected. If available, forces obtained from the GRAPE coprocessors may be transparently substituted for those obtained from the default tree based calculation. The code may be run without modification on single processors or in parallel using OpenMP compiler directives on large scale, shared memory parallel machines. In comparison to the Gadget-2 code of Springel 2005, the gravitational force calculation is $\approx 3.5 - 4.8$ times faster with VINE when run on 8 Itanium~2 processors in an SGI Altix, while producing nearly identical outcomes in our test problems. We present simulations of several test problems, including a merger simulation of two elliptical galaxies with 800000 particles.
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