---
name: "slaqz4.f"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/slaqz4.f"
---

# slaqz4.f(3)

## NAME

SRC/slaqz4.f

## SYNOPSIS

### Functions/Subroutines

subroutine **slaqz4** (ilschur, ilq, ilz, n, ilo, ihi, nshifts, nblock\_desired, sr, si, ss, a, lda, b, ldb, q, ldq, z, ldz, qc, ldqc, zc, ldzc, work, lwork, info)\
 **SLAQZ4**

## Function/Subroutine Documentation

### subroutine slaqz4 (logical, intent(in) ilschur, logical, intent(in) ilq, logical, intent(in) ilz, integer, intent(in) n, integer, intent(in) ilo, integer, intent(in) ihi, integer, intent(in) nshifts, integer, intent(in) nblock\_desired, real, dimension( \* ), intent(inout) sr, real, dimension( \* ), intent(inout) si, real, dimension( \* ), intent(inout) ss, real, dimension( lda, \* ), intent(inout) a, integer, intent(in) lda, real, dimension( ldb, \* ), intent(inout) b, integer, intent(in) ldb, real, dimension( ldq, \* ), intent(inout) q, integer, intent(in) ldq, real, dimension( ldz, \* ), intent(inout) z, integer, intent(in) ldz, real, dimension( ldqc, \* ), intent(inout) qc, integer, intent(in) ldqc, real, dimension( ldzc, \* ), intent(inout) zc, integer, intent(in) ldzc, real, dimension( \* ), intent(inout) work, integer, intent(in) lwork, integer, intent(out) info)

**SLAQZ4**

**Purpose:**

```
!>
!> SLAQZ4 Executes a single multishift QZ sweep
!>
```

**Parameters**

*ILSCHUR*

```
!>          ILSCHUR is LOGICAL
!>              Determines whether or not to update the full Schur form
!>
```

*ILQ*

```
!>          ILQ is LOGICAL
!>              Determines whether or not to update the matrix Q
!>
```

*ILZ*

```
!>          ILZ is LOGICAL
!>              Determines whether or not to update the matrix Z
!>
```

*N*

```
!>          N is INTEGER
!>          The order of the matrices A, B, Q, and Z.  N >= 0.
!>
```

*ILO*

```
!>          ILO is INTEGER
!>
```

*IHI*

```
!>          IHI is INTEGER
!>
```

*NSHIFTS*

```
!>          NSHIFTS is INTEGER
!>          The desired number of shifts to use
!>
```

*NBLOCK\_DESIRED*

```
!>          NBLOCK_DESIRED is INTEGER
!>          The desired size of the computational windows
!>
```

*SR*

```
!>          SR is REAL array. SR contains
!>          the real parts of the shifts to use.
!>
```

*SI*

```
!>          SI is REAL array. SI contains
!>          the imaginary parts of the shifts to use.
!>
```

*SS*

```
!>          SS is REAL array. SS contains
!>          the scale of the shifts to use.
!>
```

*A*

```
!>          A is REAL array, dimension (LDA, N)
!>
```

*LDA*

```
!>          LDA is INTEGER
!>          The leading dimension of the array A.  LDA >= max( 1, N ).
!>
```

*B*

```
!>          B is REAL array, dimension (LDB, N)
!>
```

*LDB*

```
!>          LDB is INTEGER
!>          The leading dimension of the array B.  LDB >= max( 1, N ).
!>
```

*Q*

```
!>          Q is REAL array, dimension (LDQ, N)
!>
```

*LDQ*

```
!>          LDQ is INTEGER
!>
```

*Z*

```
!>          Z is REAL array, dimension (LDZ, N)
!>
```

*LDZ*

```
!>          LDZ is INTEGER
!>
```

*QC*

```
!>          QC is REAL array, dimension (LDQC, NBLOCK_DESIRED)
!>
```

*LDQC*

```
!>          LDQC is INTEGER
!>
```

*ZC*

```
!>          ZC is REAL array, dimension (LDZC, NBLOCK_DESIRED)
!>
```

*LDZC*

```
!>          LDZ is INTEGER
!>
```

*WORK*

```
!>          WORK is REAL array, dimension (MAX(1,LWORK))
!>          On exit, if INFO >= 0, WORK(1) returns the optimal LWORK.
!>
```

*LWORK*

```
!>          LWORK is INTEGER
!>          The dimension of the array WORK.  LWORK >= max(1,N).
!>
!>          If LWORK = -1, then a workspace query is assumed; the routine
!>          only calculates the optimal size of the WORK array, returns
!>          this value as the first entry of the WORK array, and no error
!>          message related to LWORK is issued by XERBLA.
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0: successful exit
!>          < 0: if INFO = -i, the i-th argument had an illegal value
!>
```

**Author**

Thijs Steel, KU Leuven

**Date**

May 2020

Definition at line **210** of file **slaqz4.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.