Man page - las2(3)

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Manual

las2

NAME
SYNOPSIS
Functions
Detailed Description
Function Documentation
subroutine dlas2 (double precision f, double precision g, double precisionh, double precision ssmin, double precision ssmax)
subroutine slas2 (real f, real g, real h, real ssmin, real ssmax)
Author

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 precisionh, 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.

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.

Author

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