# dlasq4.f

Section: LAPACK (3)
Updated: Tue Nov 14 2017
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dlasq4.f

## SYNOPSIS

### Functions/Subroutines

subroutine dlasq4 (I0, N0, Z, PP, N0IN, DMIN, DMIN1, DMIN2, DN, DN1, DN2, TAU, TTYPE, G)
DLASQ4 computes an approximation to the smallest eigenvalue using values of d from the previous transform. Used by sbdsqr.

## Function/Subroutine Documentation

### subroutine dlasq4 (integer I0, integer N0, double precision, dimension( * ) Z, integer PP, integer N0IN, double precision DMIN, double precision DMIN1, double precision DMIN2, double precision DN, double precision DN1, double precision DN2, double precision TAU, integer TTYPE, double precision G)

DLASQ4 computes an approximation to the smallest eigenvalue using values of d from the previous transform. Used by sbdsqr.

Purpose:

``` DLASQ4 computes an approximation TAU to the smallest eigenvalue
using values of d from the previous transform.
```

Parameters:

I0

```          I0 is INTEGER
First index.
```

N0

```          N0 is INTEGER
Last index.
```

Z

```          Z is DOUBLE PRECISION array, dimension ( 4*N0 )
Z holds the qd array.
```

PP

```          PP is INTEGER
PP=0 for ping, PP=1 for pong.
```

N0IN

```          N0IN is INTEGER
The value of N0 at start of EIGTEST.
```

DMIN

```          DMIN is DOUBLE PRECISION
Minimum value of d.
```

DMIN1

```          DMIN1 is DOUBLE PRECISION
Minimum value of d, excluding D( N0 ).
```

DMIN2

```          DMIN2 is DOUBLE PRECISION
Minimum value of d, excluding D( N0 ) and D( N0-1 ).
```

DN

```          DN is DOUBLE PRECISION
d(N)
```

DN1

```          DN1 is DOUBLE PRECISION
d(N-1)
```

DN2

```          DN2 is DOUBLE PRECISION
d(N-2)
```

TAU

```          TAU is DOUBLE PRECISION
This is the shift.
```

TTYPE

```          TTYPE is INTEGER
Shift type.
```

G

```          G is DOUBLE PRECISION
G is passed as an argument in order to save its value between
calls to DLASQ4.
```

Author:

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Date:

June 2016

Further Details:

```  CNST1 = 9/16
```

Definition at line 153 of file dlasq4.f.

## Author

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