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Slight numerical stability improvement in 2x2 svd

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This commit is contained in:
Gael Guennebaud 2015-03-27 10:55:00 +01:00
parent 3d59ae0203
commit 1b8cc9af43
1 changed files with 6 additions and 3 deletions
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9
Eigen/src/SVD/JacobiSVD.h
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@ -425,12 +425,13 @@ void real_2x2_jacobi_svd(const MatrixType& matrix, Index p, Index q,
// If d!=0, then t/d cannot overflow because the magnitude of the
// entries forming d are not too small compared to the ones forming t.
RealScalar u = t / d;
rot1.s() = RealScalar(1) / sqrt(RealScalar(1) + numext::abs2(u));
rot1.c() = rot1.s() * u;
RealScalar tmp = sqrt(RealScalar(1) + numext::abs2(u));
rot1.s() = RealScalar(1) / tmp;
rot1.c() = u / tmp;
}
m.applyOnTheLeft(0,1,rot1);
j_right->makeJacobi(m,0,1);
*j_left = rot1 * j_right->transpose();
*j_left = rot1 * j_right->transpose();
}
template<typename _MatrixType, int QRPreconditioner>
@ -680,6 +681,8 @@ JacobiSVD<MatrixType, QRPreconditioner>::compute(const MatrixType& matrix, unsig
const RealScalar precision = RealScalar(2) * NumTraits<Scalar>::epsilon();
// limit for very small denormal numbers to be considered zero in order to avoid infinite loops (see bug 286)
// FIXME What about considerering any denormal numbers as zero, using:
// const RealScalar considerAsZero = (std::numeric_limits<RealScalar>::min)();
const RealScalar considerAsZero = RealScalar(2) * std::numeric_limits<RealScalar>::denorm_min();
// Scaling factor to reduce over/under-flows