=========================================================================
README
=========================================================================

    Copyright (C) 2012  Edison Montoya, eamonto@gmail.com

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.


Up to date: 28 Feb 2012					

=========================================================================


This program evolve a N-body system that interacts gravitationally,
using the particle-particle approach. In this file are specified the files, 
functions and how use the program.
 
To compile the program execute in the terminal:

$make


To run the program execute:

$make run


It need to be spefied the global variables into the Makefile

INITFILE = init.txt
INPUTFILE = entrada.dat
OUTPUTFILE = salida

(this are the default values). Doing this, the program look for the 
input file (INPUTFILE) and write the output in the directory (OUTOUTFILE)
that is created by the program.


The program is execute as

$./exec <initfile> <inputfile> <outputfile>


exec         --> executable 

<initfile>   --> Parameters of the system

<inputfile>  --> Initial conditions for the system, order:
	         radial distance, position x, y, z, velocity x, y, z, mass.

<outputfile> --> Name of the output directory.


esample:
./exec.out init.txt input.dat outputfile


All the outputs are write into the directory "outputfile", the files are:

* A copy of the parameters file (INITFILE).

* Files with the evolution of the system <outputfile>_#.dat, the data
  are arranged as:
  radius, position x, y, z, velocity x, y, z, mass.  


The files into this repository are:


========================================================================
init.txt
========================================================================
Contains the parameters, namely,

1000          NUMBER OF PARTICLES
0.005         TIME STEP
1.0           GRAVITATIONAL CONSTANT
0.0           ROTATION
1.0	      NUMBER OF OUTPUT FILES
1.0	      NUMBER OF INTEGRATION PER FILE
0.16	      SOFTENING LENGHT (EPS) 
0	      ELECTION OF INTEGRATOR, 0=SYMPLECTIC, 1=RK4


Note: The RK4 integrations is already not implemented.


========================================================================
input.dat
========================================================================
This file have initial conditions for 1000 particles that make a polytropic
stellar system with polytropic index n=1.5, whit this file can be run
tests of the program. The values into "init.txt" and the Makefile are for
this system. The result must be that the system remains in equilibrium.


========================================================================
main.cu
========================================================================
This is the main file, from here are coordinated all the operations, namely,
evolution in time and communications between CPU and GPU. All the global
variables in the CPU are defined here. The program evolves the system 
using a symplectic integrator (leapfrog).



=========================================================================
lib_io.c
=========================================================================
Into this file are implemented all the input-output routines.


///////////VERIFICATION OF INPUT FILES/////////////
int usage(void)

//REMOVE OLD outputfile AND CREATE A NEW ONE
int create_remove_dir(void)

////////READ PARAMETERS OF THE SYSTEM/////
int read(void)

//////////////////////READ INITIAL POSITIONS AND VELOCITIES////////////////////
int read_input(void)

////////////WRITE RADIUS, POSITIONS, VELOCITIES AND MASS/////////////////////
int write_output(int j)

/////////FREE MEMORY THAT WAS ALLOCATE IN THE CPU///////////
int free_CPU_memory(void)



=========================================================================
lib_N_body.cu
=========================================================================
Set of functions that runs in the GPU, namely, the integration in time
of particles positions and the calculation of aceleration using the
particle-particle approach. The routines are:


//EVOLUTION OF POSITIONS USING THE leapfrog ALGORITHM
__global__ void cuda_pos(float *dt, float *vel0, float *vel1, float *vel2, 
	   float *pos0, float *pos1, float *pos2)


//////////////// ACELERATION(in variable acele) OF PARTICLE i////////////////
__global__ void cuda_aceleration (int *i, float *eps, float *G, float *dt, 
	   float *mass, float *pos0, float *pos1, float *pos2, 
	   float *vel0, float *vel1, float *vel2, float *acele0, 
	   float *acele1, float *acele2)