C++ MATRIX::size2方法代码示例

size_t cholesky_decompose(const MATRIX& A, TRIA& L)
{
  using namespace ublas;

  assert( A.size1() == A.size2() );
  assert( A.size1() == L.size1() );
  assert( A.size2() == L.size2() );

  const size_t n = A.size1();

  for (size_t k=0 ; k < n; k++) {

    double qL_kk = A(k,k) - inner_prod( project( row(L, k), range(0, k) ),
                                        project( row(L, k), range(0, k) ) );

    if (qL_kk <= 0) {
      return 1 + k;
    } else {
      double L_kk = sqrt( qL_kk );
      L(k,k) = L_kk;

      matrix_column<TRIA> cLk(L, k);
      project( cLk, range(k+1, n) )
        = ( project( column(A, k), range(k+1, n) )
            - prod( project(L, range(k+1, n), range(0, k)),
                    project(row(L, k), range(0, k) ) ) ) / L_kk;
    }
  }
  return 0;
}

template<typename MATRIX> MATRIX expm_pad(const MATRIX &H, typename type_traits<typename MATRIX::value_type>::real_type t = 1.0, const int p = 6){
	typedef typename MATRIX::value_type value_type;
        typedef typename MATRIX::size_type size_type;
	typedef typename type_traits<value_type>::real_type real_value_type;
	assert(H.size1() == H.size2());
	assert(p >= 1);
	const size_type n = H.size1();
	const identity_matrix<value_type> I(n);
	matrix<value_type> U(n,n),H2(n,n),P(n,n),Q(n,n);
	real_value_type norm = 0.0;
// Calcuate Pade coefficients
	vector<real_value_type> c(p+1);
	c(0)=1;  
	for(size_type i = 0; i < (size_type) p; ++i) 
		c(i+1) = c(i) * ((p - i)/((i + 1.0) * (2.0 * p - i)));
// Calcuate the infinty norm of H, which is defined as the largest row sum of a matrix
	for(size_type i=0; i<n; ++i) {
		real_value_type temp = 0.0;
		for(size_type j = 0; j < n; j++)
			temp += std::abs(H(i, j)); 
		norm = t * std::max<real_value_type>(norm, temp);
	}
// If norm = 0, and all H elements are not NaN or infinity but zero, 
// then U should be identity.
	if (norm == 0.0) {
		bool all_H_are_zero = true;
		for(size_type i = 0; i < n; i++)
			for(size_type j = 0; j < n; j++)
				if( H(i,j) != value_type(0.0) ) 
					all_H_are_zero = false; 
		if( all_H_are_zero == true ) return I;
// Some error happens, H has elements which are NaN or infinity. 
		std::cerr<<"Null input error in the template expm_pad.\n";
		//		std::cout << "Null INPUT : " << H <<"\n";
		exit(0);
	}
// Scaling, seek s such that || H*2^(-s) || < 1/2, and set scale = 2^(-s)
 	int s = 0;
	real_value_type scale = 1.0;
	if(norm > 0.5) {
		s = std::max<int>(0, static_cast<int>((log(norm) / log(2.0) + 2.0)));
		scale /= real_value_type(std::pow(2.0, s));
		U.assign((scale * t) * H); // Here U is used as temp value due to that H is const
	}
	else
		U.assign(H);

// Horner evaluation of the irreducible fraction, see the following ref above.
// Initialise P (numerator) and Q (denominator) 
	H2.assign( prod(U, U) );
	Q.assign( c(p)*I );
	P.assign( c(p-1)*I );
	size_type odd = 1;
	for( size_type k = p - 1; k > 0; --k) {
		( odd == 1 ) ?
			( Q = ( prod(Q, H2) + c(k-1) * I ) ) :
			( P = ( prod(P, H2) + c(k-1) * I ) ) ;
		odd = 1 - odd;
	}
	( odd == 1 ) ? ( Q = prod(Q, U) ) : ( P = prod(P, U) );
	Q -= P;
// In origine expokit package, they use lapack ZGESV to obtain inverse matrix,
// and in that ZGESV routine, it uses LU decomposition for obtaing inverse matrix.
// Since in ublas, there is no matrix inversion template, I simply use the build-in
// LU decompostion package in ublas, and back substitute by myself.

// Implement Matrix Inversion
	permutation_matrix<size_type> pm(n); 
	int res = lu_factorize(Q, pm);
	if( res != 0) {
		std::cerr << "Matrix inversion error in the template expm_pad.\n";
		exit(0);
	}
// H2 is not needed anymore, so it is temporary used as identity matrix for substituting.
	H2.assign(I); 
	lu_substitute(Q, pm, H2); 
	(odd == 1) ? 
		( U.assign( -(I + real_value_type(2.0) * prod(H2, P))) ):
		( U.assign(   I + real_value_type(2.0) * prod(H2, P) ) );
// Squaring 
	for(size_type i = 0; i < (size_type) s; ++i)
		U = (prod(U,U));
	return U;
}