// Cnuderiv.java  non uniformly spaced x[] derivative coefficients cx[]
//                needs Complex.java Cinvert.java compiled 
// new Cnuderiv(order, npoints, point, x[], cx[]) cx returned
// discrete derivative is sum f(x[])*cx[])

class Cnuderiv
{
  Complex Czero = new Complex(0.0,0.0);
  Complex Cone  = new Complex(1.0,0.0);

  Cnuderiv(int order, int npoint, int point, Complex x[], Complex c[])
  {
    int n = npoint;
    Complex A[][] = new Complex[n][n];
    Complex fct[] = new Complex[n];
    Complex pwr;

    for(int i=0; i<n; i++) // build matrix that will be inverted 
    {
      pwr=Cone;
      for(int j=0; j<n; j++)
      {
        A[i][j] = pwr;
        pwr = pwr.multiply(x[i]);
      }
    }
    new Cinvert(A); // invert the matrix 
    // form derivative for order and point 
    for(int i=0; i<n; i++) // compute factors for order 
    {
      fct[i] = Cone;
    }
    for(int j=0; j<order; j++)
    {
      for(int i=0; i<n; i++)
      {
        fct[i] = fct[i].multiply(new Complex((double)(i-j),0.0));
      }
    }
    for(int i=0; i<n; i++)
    {
      c[i] = Czero;
      pwr = Cone;
      for(int j=order; j<n; j++)
      { 
	c[i] = c[i].add(fct[j].multiply(A[j][i].multiply(pwr)));
        pwr = pwr.multiply(x[point]);
      }
    }
  } // end Cnuderiv 
} // end class Cnuderiv