# claqr1 (3) - Linux Man Pages

claqr1.f -

## SYNOPSIS

### Functions/Subroutines

subroutine claqr1 (N, H, LDH, S1, S2, V)
CLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.

## Function/Subroutine Documentation

### subroutine claqr1 (integerN, complex, dimension( ldh, * )H, integerLDH, complexS1, complexS2, complex, dimension( * )V)

CLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.

Purpose:

```      Given a 2-by-2 or 3-by-3 matrix H, CLAQR1 sets v to a
scalar multiple of the first column of the product

(*)  K = (H - s1*I)*(H - s2*I)

scaling to avoid overflows and most underflows.

This is useful for starting double implicit shift bulges
in the QR algorithm.
```

Parameters:

N

```          N is integer
Order of the matrix H. N must be either 2 or 3.
```

H

```          H is COMPLEX array of dimension (LDH,N)
The 2-by-2 or 3-by-3 matrix H in (*).
```

LDH

```          LDH is integer
The leading dimension of H as declared in
the calling procedure.  LDH.GE.N
```

S1

```          S1 is COMPLEX
```

S2

```          S2 is COMPLEX

S1 and S2 are the shifts defining K in (*) above.
```

V

```          V is COMPLEX array of dimension N
A scalar multiple of the first column of the
matrix K in (*).
```

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Contributors:

Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA

Definition at line 108 of file claqr1.f.

## Author

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