# zlaic1 (3) - Linux Man Pages

zlaic1.f -

## SYNOPSIS

### Functions/Subroutines

subroutine zlaic1 (JOB, J, X, SEST, W, GAMMA, SESTPR, S, C)
ZLAIC1 applies one step of incremental condition estimation.

## Function/Subroutine Documentation

### subroutine zlaic1 (integerJOB, integerJ, complex*16, dimension( j )X, double precisionSEST, complex*16, dimension( j )W, complex*16GAMMA, double precisionSESTPR, complex*16S, complex*16C)

ZLAIC1 applies one step of incremental condition estimation.

Purpose:

``` ZLAIC1 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 ZLAIC1 computes sestpr, s, c such that
the vector
[ s*x ]
xhat = [  c  ]
is an approximate singular vector of
[ L       0  ]
Lhat = [ w**H 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]**H and sestpr**2 is an eigenpair of the system

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

where  alpha =  x**H * 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 COMPLEX*16 array, dimension (J)
The j-vector x.
```

SEST

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

W

```          W is COMPLEX*16 array, dimension (J)
The j-vector w.
```

GAMMA

```          GAMMA is COMPLEX*16
The diagonal element gamma.
```

SESTPR

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

S

```          S is COMPLEX*16
Sine needed in forming xhat.
```

C

```          C is COMPLEX*16
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 136 of file zlaic1.f.

## Author

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