log.txt

template<class Coord>
inline R4MatrixTC<Coord> R4MatrixTC<Coord>::Log( ) const
{
   R4MatrixTC<Coord> A = (*this);           // call it A to be like Alexa's pseudocode
   R4MatrixTC<Coord> I; I.MakeIdentity();   // identity matrix
   //A.PrintMatlab();

   int k = 0;
   int n1 = 30;
   double eps1 = 0.0001;
   while ((A-I).NormF() > eps1 /*&& k < in_n*/ ) {
      double error = (A-I).NormF();
      A = A.Sqrt();
      k++;

      if (k > n1) {
         printf("log: repeated square roots failed to converge after %d iterations\n", n1);
         break;
      }
   }

   A = A - I;
   R4MatrixTC<Coord> Z = A;
   R4MatrixTC<Coord> X = A;
   Coord i = 1.0;
   double eps2 = 0.000000001;
   int n2 = 7;

   while ( Z.NormF() > eps2 ) {
      Z = Z*A;
      i++;
      X = X + Z/i;
      if (i > n2) { 
         printf("log: failed to converge after %d iterations\n", n2);
         break;
      }
   }

   X = (Coord)pow(2.0,k)*X;
   return X;
}