---
name: "claqz2.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/claqz2.f"
---

# claqz2.f(3)

## NAME

SRC/claqz2.f

## SYNOPSIS

### Functions/Subroutines

recursive subroutine **claqz2** (ilschur, ilq, ilz, n, ilo, ihi, nw, a, lda, b, ldb, q, ldq, z, ldz, ns, nd, alpha, beta, qc, ldqc, zc, ldzc, work, lwork, rwork, rec, info)\
 **CLAQZ2**

## Function/Subroutine Documentation

### recursive subroutine claqz2 (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) nw, complex, dimension( lda, \* ), intent(inout) a, integer, intent(in) lda, complex, dimension( ldb, \* ), intent(inout) b, integer, intent(in) ldb, complex, dimension( ldq, \* ), intent(inout) q, integer, intent(in) ldq, complex, dimension( ldz, \* ), intent(inout) z, integer, intent(in) ldz, integer, intent(out) ns, integer, intent(out) nd, complex, dimension( \* ), intent(inout) alpha, complex, dimension( \* ), intent(inout) beta, complex, dimension( ldqc, \* ) qc, integer, intent(in) ldqc, complex, dimension( ldzc, \* ) zc, integer, intent(in) ldzc, complex, dimension( \* ) work, integer, intent(in) lwork, real, dimension( \* ) rwork, integer, intent(in) rec, integer, intent(out) info)

**CLAQZ2**

**Purpose:**

```
!>
!> CLAQZ2 performs AED
!>
```

**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
!>          ILO and IHI mark the rows and columns of (A,B) which
!>          are to be normalized
!>
```

*NW*

```
!>          NW is INTEGER
!>          The desired size of the deflation window.
!>
```

*A*

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

*LDA*

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

*B*

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

*LDB*

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

*Q*

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

*LDQ*

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

*Z*

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

*LDZ*

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

*NS*

```
!>          NS is INTEGER
!>          The number of unconverged eigenvalues available to
!>          use as shifts.
!>
```

*ND*

```
!>          ND is INTEGER
!>          The number of converged eigenvalues found.
!>
```

*ALPHA*

```
!>          ALPHA is COMPLEX array, dimension (N)
!>          Each scalar alpha defining an eigenvalue
!>          of GNEP.
!>
```

*BETA*

```
!>          BETA is COMPLEX array, dimension (N)
!>          The scalars beta that define the eigenvalues of GNEP.
!>          Together, the quantities alpha = ALPHA(j) and
!>          beta = BETA(j) represent the j-th eigenvalue of the matrix
!>          pair (A,B), in one of the forms lambda = alpha/beta or
!>          mu = beta/alpha.  Since either lambda or mu may overflow,
!>          they should not, in general, be computed.
!>
```

*QC*

```
!>          QC is COMPLEX array, dimension (LDQC, NW)
!>
```

*LDQC*

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

*ZC*

```
!>          ZC is COMPLEX array, dimension (LDZC, NW)
!>
```

*LDZC*

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

*WORK*

```
!>          WORK is COMPLEX 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.
!>
```

*RWORK*

```
!>          RWORK is REAL array, dimension (N)
!>
```

*REC*

```
!>          REC is INTEGER
!>             REC indicates the current recursion level. Should be set
!>             to 0 on first call.
!>
```

*INFO*

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

**Author**

Thijs Steel, KU Leuven, KU Leuven

**Date**

May 2020

Definition at line **231** of file **claqz2.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.