void stiff_deriv ( double t, double y[], double dydt[] );
double *stiff_exact ( int n, double t[] );
void stiff_parameters ( 
  double *lambda_in,  double *t0_in,  double *y0_in,  double *tstop_in, 
  double *lambda_out, double *t0_out, double *y0_out, double *tstop_out );