dlaic1.f - Man Page

SRC/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 (integer job, integer j, double precision, dimension( j ) x, double precision sest, double precision, dimension( j ) w, double precision gamma, double precision sestpr, double precision s, double precision c)

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.

Definition at line 133 of file dlaic1.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

The man page dlaic1(3) is an alias of dlaic1.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK