# ?lasq4

Computes an approximation to the smallest eigenvalue using values of d from the previous transform. Used by ?bdsqr.

## Syntax

call slasq4( i0, n0, z, pp, n0in, dmin, dmin1, dmin2, dn, dn1, dn2, tau, ttype )

call dlasq4( i0, n0, z, pp, n0in, dmin, dmin1, dmin2, dn, dn1, dn2, tau, ttype )

## Description

The routine computes an approximation tau to the smallest eigenvalue using values of d from the previous transform.

## Input Parameters

i0

  INTEGER. First index.

n0

  INTEGER. Last index.

z

  REAL for slasq4

  DOUBLE PRECISION for dlasq4.

  Array, DIMENSION (4n).

  Z holds the qd array.

pp

  INTEGER. `pp=0` for ping, `pp=1` for pong.

n0in

  INTEGER. The value of n0 at start of eigtest.

dmin

  REAL for slasq4

  DOUBLE PRECISION for dlasq4.

  Minimum value of d.

dmin1

  REAL for slasq4

  DOUBLE PRECISION for dlasq4.

  Minimum value of d, excluding d(n0).

dmin2

  REAL for slasq4

  DOUBLE PRECISION for dlasq4.

  Minimum value of d, excluding d(n0)

  and d(n0-1).

dn

  REAL for slasq4

  DOUBLE PRECISION for dlasq4. Contains d(n).

dn1

  REAL for slasq4

  DOUBLE PRECISION for dlasq4. Contains d(n-1).

dn2

  REAL for slasq4

  DOUBLE PRECISION for dlasq4. Contains d(n-2).

## Output Parameters

tau

  REAL for slasq4

  DOUBLE PRECISION for dlasq4.

  Shift.

ttype

  INTEGER. Shift type.

Parent topic: Auxiliary Routines