/* Sample C code for homework 3 
 *
 * to compile it, type
 *
 * cc hw3.c -o hw3 -lm
 *
 */

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

main() {

  float x[2],t,dt;  /* declare the variables */
  float tfinal;

  FILE *fp;

  tfinal = 50.0;
  dt = 0.001;


  /* initial conditions */
  x[0] = 0.0;
  x[1] = 0.1;

  /* open data.d to be written */
  fp = fopen("data.d","w");

  for(t=0;t<=tfinal;t+=dt) {

    x[0] += x[1]*dt;
    x[1] += (-0.25*x[1] + x[0] - pow(x[0],3) + 0.3*cos(t))*dt;
    /* print data to data.d */
    fprintf(fp,"%f \t %f \t %f \n",t,x[0],x[1]);
  }

  /* close data.d */
  fclose(fp);
}