/* ------------------------------------------------------------------------
 * SERIAL Concurrent Wave Equation - C Version
 * FILE: ser_wave.c
 * DESCRIPTION:
 *   This program implements the concurrent wave equation described 
 *   in Chapter 5 of Fox et al., 1988, Solving Problems on Concurrent
 *   Processors, vol 1.  
 *
 *   A vibrating string is decomposed into points.  In the parallel
 *   version each processor is responsible for updating the amplitude 
 *   of a number of points over time.
 *	
 *   At each iteration, each processor exchanges boundary points with
 *   nearest neighbors.  This version uses low level sends and receives
 *   to exchange boundary points.
 *
 * LAST REVISED:  11/25/95  Blaise Barney
 * ------------------------------------------------------------------------*/

#include <stdlib.h>
#include <math.h>
#include <stdio.h>
#include <time.h>

#define MAXPOINTS 1000
#define MAXSTEPS 10000
#define MINPOINTS 20
#define PI 3.14159265


void init_param(void);
void init_line(void);
void update (void);

int nsteps,                 	/* number of time steps */
    tpoints, 		     		/* total points along string */
    rcode;                  	/* generic return code */
double values[MAXPOINTS+2], 	/* values at time t */
       oldval[MAXPOINTS+2], 	/* values at time (t-dt) */
       newval[MAXPOINTS+2]; 	/* values at time (t+dt) */

/*  ------------------------------------------------------------------------
 *	Obtains input values from user
 *  ------------------------------------------------------------------------ */

void init_param(void)
     {

 char tchar[8];

     /* set number of points, number of iterations */
     tpoints = 0;
     nsteps = 0;
     while ((tpoints < MINPOINTS) || (tpoints > MAXPOINTS))
          {
          printf("Enter number of points along vibrating string\n");
          scanf("%s", tchar);
	  tpoints = atoi(tchar);
          if ((tpoints < MINPOINTS) || (tpoints > MAXPOINTS))
               printf("enter value between %d and %d\n", MINPOINTS, MAXPOINTS);
          }
     while ((nsteps < 1) || (nsteps > MAXSTEPS))
          {
          printf("Enter number of time steps\n");
          scanf("%s", tchar);
	  nsteps = atoi(tchar);
          if ((nsteps < 1) || (nsteps > MAXSTEPS))
               printf("enter value between 1 and %d\n", MAXSTEPS);
          }

     printf("points = %d, steps = %d\n", tpoints, nsteps);

     }
/*  ------------------------------------------------------------------------
 *     All processes initialize points on line
 *  --------------------------------------------------------------------- */

void init_line(void)
     {
     int i, j, k;
     double x, fac;

     /* calculate initial values based on sine curve */

     fac = 2.0 * PI;
     k = 0; 
       for (j = 1; j <= tpoints; j++, k++)
         {
         x = (double)k/(double)(tpoints - 1);
         values[j] = sin (fac * x);
         } 
     for (i = 1; i <= tpoints; i++) oldval[i] = values[i];
     }

/*  -------------------------------------------------------------------------
 *      Calculate new values using wave equation
 *  -------------------------------------------------------------------------*/
 
void do_math(int i)
     {
     double dtime, c, dx, tau, sqtau;

     dtime = 0.3;
     c = 1.0;
     dx = 1.0;
     tau = (c * dtime / dx);
     sqtau = tau * tau;
     newval[i] = (2.0 * values[i]) - oldval[i] 
                + (sqtau * (values[i-1] - (2.0 * values[i]) + values[i+1]));
     }

/*  -------------------------------------------------------------------------
 *	Update the points a specified number of times 
 *  -------------------------------------------------------------------------*/
 
void update()
     {
     int i, j, tpts;

     /* update values for each point along string */
	  /* update points along line */
          for (j = 1; j <= tpoints; j++)
               {
               /* global endpoints */
               if ((j == 1) || (j  == tpoints))
                    newval[j] = 0.0;
	       else
                    do_math(j);
 	       }
          for (j = 1; j <= tpoints; j++)
               {
               oldval[j] = values[j];
	       values[j] = newval[j];
	       }
          

/* print it out for validation */

     tpts = (tpoints < 10) ? tpoints: 10; 
     printf("first %d points (for validation):\n", tpts);
     for (i = 0; i < tpts; i++) printf("%4.2f  ", values[i]);
     printf("\n");

     }


/*  ------------------------------------------------------------------------
 *	Main program
 *  ------------------------------------------------------------------------ */

main()
     {
     int left, right;


     /* get program parameters and initialize wave values */
     init_param();
     init_line();

     /* update values along the line for nstep time steps */
     update();


     return 0;
     }