void ctof ( int nc, double uc[], int nf, double uf[] );
void ftoc ( int nf, double uf[], double rf[], int nc, double uc[], 
  double rc[] );
void gauss_seidel ( int n, double r[], double u[], double *dif_l1 );
int i4_log_2 ( int i );
int i4_power ( int i, int j );
void poisson_1d_monogrid ( int n, double a, double b, double ua, double ub,
  double force ( double x ), double exact ( double x ), int *it_num,
  double u[] );
void poisson_1d_multigrid ( int n, double a, double b, double ua, double ub,
  double force ( double x ), double exact ( double x ), int *it_num, 
  double u[] );
double *r8vec_linspace_new ( int n, double a, double b );