# DLAIC1 (3) - Linux Manuals

dlaic1.f -

## SYNOPSIS

### Functions/Subroutines

subroutine dlaic1 (JOB, J, X, SEST, W, GAMMA, SESTPR, S, C)
DLAIC1 applies one step of incremental condition estimation.

## Function/Subroutine Documentation

### subroutine dlaic1 (integerJOB, integerJ, double precision, dimension( j )X, double precisionSEST, double precision, dimension( j )W, double precisionGAMMA, double precisionSESTPR, double precisionS, double precisionC)

DLAIC1 applies one step of incremental condition estimation.

Purpose:

DLAIC1 applies one step of incremental condition estimation in
its simplest version:

Let x, twonorm(x) = 1, be an approximate singular vector of an j-by-j
lower triangular matrix L, such that
twonorm(L*x) = sest
Then DLAIC1 computes sestpr, s, c such that
the vector
[ s*x ]
xhat = [  c  ]
is an approximate singular vector of
[ L       0  ]
Lhat = [ w**T gamma ]
in the sense that
twonorm(Lhat*xhat) = sestpr.

Depending on JOB, an estimate for the largest or smallest singular
value is computed.

Note that [s c]**T and sestpr**2 is an eigenpair of the system

diag(sest*sest, 0) + [alpha  gamma] * [ alpha ]
[ gamma ]

where  alpha =  x**T*w.

Parameters:

JOB

JOB is INTEGER
= 1: an estimate for the largest singular value is computed.
= 2: an estimate for the smallest singular value is computed.

J

J is INTEGER
Length of X and W

X

X is DOUBLE PRECISION array, dimension (J)
The j-vector x.

SEST

SEST is DOUBLE PRECISION
Estimated singular value of j by j matrix L

W

W is DOUBLE PRECISION array, dimension (J)
The j-vector w.

GAMMA

GAMMA is DOUBLE PRECISION
The diagonal element gamma.

SESTPR

SESTPR is DOUBLE PRECISION
Estimated singular value of (j+1) by (j+1) matrix Lhat.

S

S is DOUBLE PRECISION
Sine needed in forming xhat.

C

C is DOUBLE PRECISION
Cosine needed in forming xhat.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 135 of file dlaic1.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.