Eigen  3.3.3
RealSvd2x2.h
00001 // This file is part of Eigen, a lightweight C++ template library
00002 // for linear algebra.
00003 //
00004 // Copyright (C) 2009-2010 Benoit Jacob <jacob.benoit.1@gmail.com>
00005 // Copyright (C) 2013-2016 Gael Guennebaud <gael.guennebaud@inria.fr>
00006 //
00007 // This Source Code Form is subject to the terms of the Mozilla
00008 // Public License v. 2.0. If a copy of the MPL was not distributed
00009 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
00010 
00011 #ifndef EIGEN_REALSVD2X2_H
00012 #define EIGEN_REALSVD2X2_H
00013 
00014 namespace Eigen {
00015 
00016 namespace internal {
00017 
00018 template<typename MatrixType, typename RealScalar, typename Index>
00019 void real_2x2_jacobi_svd(const MatrixType& matrix, Index p, Index q,
00020                          JacobiRotation<RealScalar> *j_left,
00021                          JacobiRotation<RealScalar> *j_right)
00022 {
00023   using std::sqrt;
00024   using std::abs;
00025   Matrix<RealScalar,2,2> m;
00026   m << numext::real(matrix.coeff(p,p)), numext::real(matrix.coeff(p,q)),
00027        numext::real(matrix.coeff(q,p)), numext::real(matrix.coeff(q,q));
00028   JacobiRotation<RealScalar> rot1;
00029   RealScalar t = m.coeff(0,0) + m.coeff(1,1);
00030   RealScalar d = m.coeff(1,0) - m.coeff(0,1);
00031 
00032   if(abs(d) < (std::numeric_limits<RealScalar>::min)())
00033   {
00034     rot1.s() = RealScalar(0);
00035     rot1.c() = RealScalar(1);
00036   }
00037   else
00038   {
00039     // If d!=0, then t/d cannot overflow because the magnitude of the
00040     // entries forming d are not too small compared to the ones forming t.
00041     RealScalar u = t / d;
00042     RealScalar tmp = sqrt(RealScalar(1) + numext::abs2(u));
00043     rot1.s() = RealScalar(1) / tmp;
00044     rot1.c() = u / tmp;
00045   }
00046   m.applyOnTheLeft(0,1,rot1);
00047   j_right->makeJacobi(m,0,1);
00048   *j_left = rot1 * j_right->transpose();
00049 }
00050 
00051 } // end namespace internal
00052 
00053 } // end namespace Eigen
00054 
00055 #endif // EIGEN_REALSVD2X2_H
 All Classes Functions Variables Typedefs Enumerations Enumerator Friends