# include <cstdlib>
# include <iostream>
# include <cmath>
# include <ctime>

using namespace std;

# include "kronrod.hpp"

//****************************************************************************80

void abwe1 ( int n, int m, double eps, double coef2, bool even, double b[], 
  double *x, double *w )

//****************************************************************************80
//
//  Purpose:
//
//    ABWE1 calculates a Kronrod abscissa and weight.
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    03 August 2010
//
//  Author:
//
//    Original FORTRAN77 version by Robert Piessens, Maria Branders.
//    C++ version by John Burkardt.
//
//  Reference:
//
//    Robert Piessens, Maria Branders,
//    A Note on the Optimal Addition of Abscissas to Quadrature Formulas
//    of Gauss and Lobatto,
//    Mathematics of Computation,
//    Volume 28, Number 125, January 1974, pages 135-139.
//
//  Parameters:
//
//    Input, int N, the order of the Gauss rule.
//
//    Input, int M, the value of ( N + 1 ) / 2.
//
//    Input, double EPS, the requested absolute accuracy of the
//    abscissas.
//
//    Input, double COEF2, a value needed to compute weights.
//
//    Input, bool EVEN, is TRUE if N is even.
//
//    Input, double B[M+1], the Chebyshev coefficients.
//
//    Input/output, double *X; on input, an estimate for
//    the abscissa, and on output, the computed abscissa.
//
//    Output, double *W, the weight.
//
{
  double ai;
  double b0;
  double b1;
  double b2;
  double d0;
  double d1;
  double d2;
  double delta;
  double dif;
  double f;
  double fd;
  int i;
  int iter;
  int k;
  int ka;
  double yy;

  if ( *x == 0.0 )
  {
    ka = 1;
  }
  else
  {
    ka = 0;
  }
//
//  Iterative process for the computation of a Kronrod abscissa.
//
  for ( iter = 1; iter <= 50; iter++ )
  {
    b1 = 0.0;
    b2 = b[m];
    yy = 4.0 * (*x) * (*x) - 2.0;
    d1 = 0.0;

    if ( even )
    {
      ai = m + m + 1;
      d2 = ai * b[m];
      dif = 2.0;
    }
    else
    {
      ai = m + 1;
      d2 = 0.0;
      dif = 1.0;
    }

    for ( k = 1; k <= m; k++ )
    {
      ai = ai - dif;
      i = m - k + 1;
      b0 = b1;
      b1 = b2;
      d0 = d1;
      d1 = d2;
      b2 = yy * b1 - b0 + b[i-1];
      if ( !even )
      {
        i = i + 1;
      }
      d2 = yy * d1 - d0 + ai * b[i-1];
    }

    if ( even )
    {
      f = ( *x ) * ( b2 - b1 );
      fd = d2 + d1;
    }
    else
    {
      f = 0.5 * ( b2 - b0 );
      fd = 4.0 * ( *x ) * d2;
    }
//
//  Newton correction.
//
    delta = f / fd;
    *x = *x - delta;

    if ( ka == 1 )
    {
      break;
    }

    if ( r8_abs ( delta ) <= eps )
    {
      ka = 1;
    }
  }
//
//  Catch non-convergence.
//
  if ( ka != 1 )
  {
    cout << "\n";
    cout << "ABWE1 - Fatal error!\n";
    cout << "  Iteration limit reached.\n";
    cout << "  Last DELTA was " << delta << "\n";
    exit ( 1 );
  }
//
//  Computation of the weight.
//
  d0 = 1.0;
  d1 = *x;
  ai = 0.0;
  for ( k = 2; k <= n; k++ )
  {
    ai = ai + 1.0;
    d2 = ( ( ai + ai + 1.0 ) * ( *x ) * d1 - ai * d0 ) / ( ai + 1.0 );
    d0 = d1;
    d1 = d2;
  }

  *w = coef2 / ( fd * d2 );

  return;
}
//****************************************************************************80

void abwe2 ( int n, int m, double eps, double coef2, bool even, double b[], 
  double *x, double *w1, double *w2 )

//****************************************************************************80
//
//  Purpose:
//
//    ABWE2 calculates a Gaussian abscissa and two weights.
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    03 August 2010
//
//  Author:
//
//    Original FORTRAN77 version by Robert Piessens, Maria Branders.
//    C++ version by John Burkardt.
//
//  Reference:
//
//    Robert Piessens, Maria Branders,
//    A Note on the Optimal Addition of Abscissas to Quadrature Formulas
//    of Gauss and Lobatto,
//    Mathematics of Computation,
//    Volume 28, Number 125, January 1974, pages 135-139.
//
//  Parameters:
//
//    Input, int N, the order of the Gauss rule.
//
//    Input, int M, the value of ( N + 1 ) / 2.
//
//    Input, double EPS, the requested absolute accuracy of the
//    abscissas.
//
//    Input, double COEF2, a value needed to compute weights.
//
//    Input, bool EVEN, is TRUE if N is even.
//
//    Input, double B[M+1], the Chebyshev coefficients.
//
//    Input/output, double *X; on input, an estimate for
//    the abscissa, and on output, the computed abscissa.
//
//    Output, double *W1, the Gauss-Kronrod weight.
//
//    Output, double *W2, the Gauss weight.
//
{
  double ai;
  double an;
  double delta;
  int i;
  int iter;
  int k;
  int ka;
  double p0;
  double p1;
  double p2;
  double pd0;
  double pd1;
  double pd2;
  double yy;

  if ( *x == 0.0 )
  {
    ka = 1;
  }
  else
  {
    ka = 0;
  }
//
//  Iterative process for the computation of a Gaussian abscissa.
//
  for ( iter = 1; iter <= 50; iter++ )
  {
    p0 = 1.0;
    p1 = *x;
    pd0 = 0.0;
    pd1 = 1.0;
    ai = 0.0;
    for ( k = 2; k <= n; k++ )
    {
      ai = ai + 1.0;
      p2 = ( ( ai + ai + 1.0 ) * (*x) * p1 - ai * p0 ) / ( ai + 1.0 );
      pd2 = ( ( ai + ai + 1.0 ) * ( p1 + (*x) * pd1 ) - ai * pd0 ) 
        / ( ai + 1.0 );
      p0 = p1;
      p1 = p2;
      pd0 = pd1;
      pd1 = pd2;
    }
//
//  Newton correction.
//
    delta = p2 / pd2;
    *x = *x - delta;

    if ( ka == 1 )
    {
      break;
    }

    if ( r8_abs ( delta ) <= eps )
    {
      ka = 1;
    }
  }
//
//  Catch non-convergence.
//
  if ( ka != 1 )
  {
    cout << "\n";
    cout << "ABWE2 - Fatal error!\n";
    cout << "  Iteration limit reached.\n";
    cout << "  Last DELTA was " << delta << "\n";
    exit ( 1 );
  }
//
//  Computation of the weight.
//
  an = n;

  *w2 = 2.0 / ( an * pd2 * p0 );

  p1 = 0.0;
  p2 = b[m];
  yy = 4.0 * (*x) * (*x) - 2.0;
  for ( k = 1; k <= m; k++ )
  {
    i = m - k + 1;
    p0 = p1;
    p1 = p2;
    p2 = yy * p1 - p0 + b[i-1];
  }

  if ( even )
  {
    *w1 = *w2 + coef2 / ( pd2 * (*x) * ( p2 - p1 ) );
  }
  else
  {
    *w1 = *w2 + 2.0 * coef2 / ( pd2 * ( p2 - p0 ) );
  }

  return;
}
//****************************************************************************80

void kronrod ( int n, double eps, double x[], double w1[], double w2[] )

//****************************************************************************80
//
//  Purpose:
//
//    KRONROD adds N+1 points to an N-point Gaussian rule.
//
//  Discussion:
//
//    This subroutine calculates the abscissas and weights of the 2N+1
//    point Gauss Kronrod quadrature formula which is obtained from the 
//    N point Gauss quadrature formula by the optimal addition of N+1 points.
//
//    The optimally added points are called Kronrod abscissas.  The 
//    abscissas and weights for both the Gauss and Gauss Kronrod rules
//    are calculated for integration over the interval [-1,+1].
//
//    Since the quadrature formula is symmetric with respect to the origin,
//    only the nonnegative abscissas are calculated.
//
//    Note that the code published in Mathematics of Computation 
//    omitted the definition of the variable which is here called COEF2.
//
//  Storage:
//
//    Given N, let M = ( N + 1 ) / 2.  
//
//    The Gauss-Kronrod rule will include 2*N+1 points.  However, by symmetry,
//    only N + 1 of them need to be listed.
//
//    The arrays X, W1 and W2 contain the nonnegative abscissas in decreasing
//    order, and the weights of each abscissa in the Gauss-Kronrod and
//    Gauss rules respectively.  This means that about half the entries
//    in W2 are zero.
//
//    For instance, if N = 3, the output is:
//
//    I      X               W1              W2
//
//    1    0.960491        0.104656         0.000000   
//    2    0.774597        0.268488         0.555556    
//    3    0.434244        0.401397         0.000000
//    4    0.000000        0.450917         0.888889
//
//    and if N = 4, (notice that 0 is now a Kronrod abscissa)
//    the output is
//
//    I      X               W1              W2
//
//    1    0.976560        0.062977        0.000000   
//    2    0.861136        0.170054        0.347855    
//    3    0.640286        0.266798        0.000000   
//    4    0.339981        0.326949        0.652145    
//    5    0.000000        0.346443        0.000000
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    03 August 2010
//
//  Author:
//
//    Original FORTRAN77 version by Robert Piessens, Maria Branders.
//    C++ version by John Burkardt.
//
//  Reference:
//
//    Robert Piessens, Maria Branders,
//    A Note on the Optimal Addition of Abscissas to Quadrature Formulas
//    of Gauss and Lobatto,
//    Mathematics of Computation,
//    Volume 28, Number 125, January 1974, pages 135-139.
//
//  Parameters:
//
//    Input, int N, the order of the Gauss rule.
//
//    Input, double EPS, the requested absolute accuracy of the
//    abscissas.
//
//    Output, double X[N+1], the abscissas.
//
//    Output, double W1[N+1], the weights for 
//    the Gauss-Kronrod rule.
//
//    Output, double W2[N+1], the weights for 
//    the Gauss rule.
//
{
  double ak;
  double an;
  double *b;
  double bb;
  double c;
  double coef;
  double coef2;
  double d;
  bool even;
  int i;
  int k;
  int l;
  int ll;
  int m;
  double s;
  double *tau;
  double x1;
  double xx;
  double y;

  b = new double[((n+1)/2)+1];
  tau = new double[(n+1)/2];
  
  m = ( n + 1 ) / 2;
  even = ( 2 * m == n );

  d = 2.0;
  an = 0.0;
  for ( k = 1; k <= n; k++ )
  {
    an = an + 1.0;
    d = d * an / ( an + 0.5 );
  }
//
//  Calculation of the Chebyshev coefficients of the orthogonal polynomial.
//
  tau[0] = ( an + 2.0 ) / ( an + an + 3.0 );
  b[m-1] = tau[0] - 1.0;
  ak = an;

  for ( l = 1; l < m; l++ )
  {
    ak = ak + 2.0;
    tau[l] = ( ( ak - 1.0 ) * ak 
      - an * ( an + 1.0 ) ) * ( ak + 2.0 ) * tau[l-1] 
      / ( ak * ( ( ak + 3.0 ) * ( ak + 2.0 ) 
      - an * ( an + 1.0 ) ) );
    b[m-l-1] = tau[l];

    for ( ll = 1; ll <= l; ll++ )
    {
      b[m-l-1] = b[m-l-1] + tau[ll-1] * b[m-l+ll-1];
    }
  }

  b[m] = 1.0;
//
//  Calculation of approximate values for the abscissas.
//
  bb = sin ( 1.570796 / ( an + an + 1.0 ) );
  x1 = sqrt ( 1.0 - bb * bb );
  s = 2.0 * bb * x1;
  c = sqrt ( 1.0 - s * s );
  coef = 1.0 - ( 1.0 - 1.0 / an ) / ( 8.0 * an * an );
  xx = coef * x1;
//
//  Coefficient needed for weights.
//
//  COEF2 = 2^(2*n+1) * n// * n// / (2n+1)//
//
  coef2 = 2.0 / ( double ) ( 2 * n + 1 );
  for ( i = 1; i <= n; i++ )
  {
    coef2 = coef2 * 4.0 * ( double ) ( i ) / ( double ) ( n + i );
  }
//
//  Calculation of the K-th abscissa (a Kronrod abscissa) and the
//  corresponding weight.
//
  for ( k = 1; k <= n; k = k + 2 )
  {
    abwe1 ( n, m, eps, coef2, even, b, &xx, w1+k-1 );
    w2[k-1] = 0.0;

    x[k-1] = xx;
    y = x1;
    x1 = y * c - bb * s;
    bb = y * s + bb * c;

    if ( k == n )
    {
      xx = 0.0;
    }
    else
    {
      xx = coef * x1;
    }
//
//  Calculation of the K+1 abscissa (a Gaussian abscissa) and the
//  corresponding weights.
//
    abwe2 ( n, m, eps, coef2, even, b, &xx, w1+k, w2+k );

    x[k] = xx;
    y = x1;
    x1 = y * c - bb * s;
    bb = y * s + bb * c;
    xx = coef * x1;
  }
//
//  If N is even, we have one more Kronrod abscissa to compute,
//  namely the origin.
//
  if ( even )
  {
    xx = 0.0;
    abwe1 ( n, m, eps, coef2, even, b, &xx, w1+n );
    w2[n] = 0.0;
    x[n] = xx;
  }

  delete [] b;
  delete [] tau;

  return;
}

//****************************************************************************80

double r8_abs ( double x )

//****************************************************************************80
//
//  Purpose:
//
//    R8_ABS returns the absolute value of an R8.
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license. 
//
//  Modified:
//
//    14 November 2006
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    Input, double X, the quantity whose absolute value is desired.
//
//    Output, double R8_ABS, the absolute value of X.
//
{
  double value;

  if ( 0.0 <= x )
  {
    value = x;
  } 
  else
  {
    value = - x;
  }
  return value;
}
//****************************************************************************80

void timestamp ( )

//****************************************************************************80
//
//  Purpose:
//
//    TIMESTAMP prints the current YMDHMS date as a time stamp.
//
//  Example:
//
//    31 May 2001 09:45:54 AM
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license. 
//
//  Modified:
//
//    08 July 2009
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    None
//
{
# define TIME_SIZE 40

  static char time_buffer[TIME_SIZE];
  const struct std::tm *tm_ptr;
  size_t len;
  std::time_t now;

  now = std::time ( NULL );
  tm_ptr = std::localtime ( &now );

  len = std::strftime ( time_buffer, TIME_SIZE, "%d %B %Y %I:%M:%S %p", tm_ptr );

  std::cout << time_buffer << "\n";

  return;
# undef TIME_SIZE
}