# dlaic1.f man page

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.

**Date:**December 2016

Definition at line 136 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 14 2017 Version 3.8.0 LAPACK