// Program to use the Euler-Cromer method to incrementally solve the 
// equation for radioactive decay, for a given mean lifetime and timestep
// Author: Shawn Havery
// Creation Date: 02-28-08

// Include stuff
#include<iostream>

using namespace std;

int main() {

  const double tmax = 15.0;	// maximum time
  double N = 1;			// current fraction of radioactive nuclei
  double t = 0;			// current time
  double tau, dt;		// mean lifetime and timestep

  cerr << "Tau: ";
  cin >> tau;			// get mean lifetime
  cerr << "Timestep: ";
  cin >> dt;			// get timestep

  do {
    cout << t << " " << N << endl;	// output values
    t += dt;				// increment time
    N -= dt * N / tau;			// compute next N
  } while (t <= tmax);			// repeat until max time
}