1. Manuals
  2. Tumbleweed
  3. lapack-man
  4. las2(3)

Scroll to navigation

las2(3) Library Functions Manual las2(3)

NAME

las2 - las2: 2x2 triangular SVD

SYNOPSIS

Functions


subroutine DLAS2 (f, g, h, ssmin, ssmax)
DLAS2 computes singular values of a 2-by-2 triangular matrix. subroutine SLAS2 (f, g, h, ssmin, ssmax)
SLAS2 computes singular values of a 2-by-2 triangular matrix.

Detailed Description

Function Documentation

subroutine DLAS2 (double precision f, double precision g, double precision h, double precision ssmin, double precision ssmax)

DLAS2 computes singular values of a 2-by-2 triangular matrix.

Purpose:

!>
!> DLAS2  computes the singular values of the 2-by-2 matrix
!>    [  F   G  ]
!>    [  0   H  ].
!> On return, SSMIN is the smaller singular value and SSMAX is the
!> larger singular value.
!>

Parameters

F 

!>          F is DOUBLE PRECISION
!>          The (1,1) element of the 2-by-2 matrix.
!>

G

!>          G is DOUBLE PRECISION
!>          The (1,2) element of the 2-by-2 matrix.
!>

H

!>          H is DOUBLE PRECISION
!>          The (2,2) element of the 2-by-2 matrix.
!>

SSMIN

!>          SSMIN is DOUBLE PRECISION
!>          The smaller singular value.
!>

SSMAX

!>          SSMAX is DOUBLE PRECISION
!>          The larger singular value.
!>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Further Details:

!>
!>  Barring over/underflow, all output quantities are correct to within
!>  a few units in the last place (ulps), even in the absence of a guard
!>  digit in addition/subtraction.
!>
!>  In IEEE arithmetic, the code works correctly if one matrix element is
!>  infinite.
!>
!>  Overflow will not occur unless the largest singular value itself
!>  overflows, or is within a few ulps of overflow.
!>
!>  Underflow is harmless if underflow is gradual. Otherwise, results
!>  may correspond to a matrix modified by perturbations of size near
!>  the underflow threshold.
!>

Definition at line 104 of file dlas2.f.

subroutine SLAS2 (real f, real g, real h, real ssmin, real ssmax)

SLAS2 computes singular values of a 2-by-2 triangular matrix.

Purpose:

!>
!> SLAS2  computes the singular values of the 2-by-2 matrix
!>    [  F   G  ]
!>    [  0   H  ].
!> On return, SSMIN is the smaller singular value and SSMAX is the
!> larger singular value.
!>

Parameters

F 

!>          F is REAL
!>          The (1,1) element of the 2-by-2 matrix.
!>

G

!>          G is REAL
!>          The (1,2) element of the 2-by-2 matrix.
!>

H

!>          H is REAL
!>          The (2,2) element of the 2-by-2 matrix.
!>

SSMIN

!>          SSMIN is REAL
!>          The smaller singular value.
!>

SSMAX

!>          SSMAX is REAL
!>          The larger singular value.
!>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Further Details:

!>
!>  Barring over/underflow, all output quantities are correct to within
!>  a few units in the last place (ulps), even in the absence of a guard
!>  digit in addition/subtraction.
!>
!>  In IEEE arithmetic, the code works correctly if one matrix element is
!>  infinite.
!>
!>  Overflow will not occur unless the largest singular value itself
!>  overflows, or is within a few ulps of overflow.
!>
!>  Underflow is harmless if underflow is gradual. Otherwise, results
!>  may correspond to a matrix modified by perturbations of size near
!>  the underflow threshold.
!>

Definition at line 104 of file slas2.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Version 3.12.0 LAPACK