/*************************    Program 1.1    ****************************/
/*                                                                      */
/************************************************************************/
/* Please Note:                                                         */
/*                                                                      */
/* (1) This computer program is written by Tao Pang in conjunction with */
/*     his book, "An Introduction to Computational Physics," published  */
/*     by Cambridge University Press in 1997.                           */
/*                                                                      */
/* (2) No warranties, express or implied, are made for this program.    */
/*                                                                      */
/************************************************************************/

#include <stdio.h>
#include <math.h>
#define NMAX 10001
#define MMAX   500

main()
/* Motion of a particle under the force f(x) = -x.  N is the
   number of time steps and M is the time steps skipped between
   two output points.  Copyright (c) Tao Pang 1997. */
{
  int i;
  double pi, dt;
  double t[NMAX], x[NMAX], v[NMAX];

/* Assign constants, initial position, and initial velocity */

  pi = 4.0 * atan(1.0);  dt = 2.0*pi / (NMAX - 1.0);
  t[0] = x[0] = 0.0;  v[0] = 1.0;

/* Recursion for position and velocity */

  for (i = 0; i < NMAX; i++)
  {
    t[i+1] = dt * (i+1);
    x[i+1] = x[i] + v[i] * dt;
    v[i+1] = v[i] - x[i] * dt;
    if ((i+MMAX) % MMAX == 0)
      printf("%16.8f %16.8f %16.8f\n", t[i], x[i], v[i]);
  }
}