LAPACK

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 is DOUBLE PRECISION


          The (1,1) element of the 2-by-2 matrix.



          G is DOUBLE PRECISION


          The (1,2) element of the 2-by-2 matrix.



          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.

subroutine slas2 (real f, real g, real h, real ssmin, real ssmax)¶

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