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

/* {{d^2} \over {dt^2}} y + y = \sin(at) */


main() {
  osci();
}

osci() {
  double X1, X2, X3, A, T, Dt;
  X1 = 0.5; X2 = 0.501; A=0.5;

  Dt = 0.07; T = 0;
  while (T<50) {
     X3 = 2*X2-X1+Dt*Dt*(sin(A*T)-X2);
	 printf("T=%lf, X1=%lf\n",T,X1);
     T=T+Dt;
     X1=X2; X2=X3;
  }
}