/* 1D FDTD simulation with an additive source. */

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

#define SIZE 200

int main()
{
  double ez[SIZE] = {0.}, hy[SIZE] = {0.}, imp0 = 377.0;
  int qTime, maxTime = 451, mm;

  char basename[80] = "sim", filename[100];
  int frame = 0;
  FILE *snapshot;

  /* do time stepping */
  for (qTime = 0; qTime < maxTime; qTime++) {
                                                  
    /* update magnetic field */                   
    for (mm = 0; mm < SIZE - 1; mm++)
      hy[mm] = hy[mm] + (ez[mm + 1] - ez[mm]) / imp0;
                                                  
    /* update electric field */                   
    for (mm = 1; mm < SIZE; mm++)
      ez[mm] = ez[mm] + (hy[mm] - hy[mm - 1]) * imp0;

    /* use additive source at node 50 */
    ez[50] += exp(-(qTime - 30.) * (qTime - 30.) / 100.); 

    /* write snapshot if time a multiple of 10 */
    if (qTime % 10 == 0) {
      sprintf(filename, "%s.%d", basename, frame++);
      snapshot=fopen(filename, "w");
      for (mm = 0; mm < SIZE; mm++)
        fprintf(snapshot, "%g\n", ez[mm]);
      fclose(snapshot);
    }
  } /* end of time-stepping */

  return 0;
}