---
name: "ungl2"
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/ungl2"
---

# ungl2(3)

{un,or}gl2: generate explicit Q, level 2, step in unglq

## NAME

ungl2 - {un,or}gl2: generate explicit Q, level 2, step in unglq

## SYNOPSIS

### Functions

subroutine **cungl2** (m, n, k, a, lda, tau, work, info)\
 **CUNGL2** generates all or part of the unitary matrix Q from an LQ factorization determined by cgelqf (unblocked algorithm).  subroutine **dorgl2** (m, n, k, a, lda, tau, work, info)\
 **DORGL2**  subroutine **sorgl2** (m, n, k, a, lda, tau, work, info)\
 **SORGL2**  subroutine **zungl2** (m, n, k, a, lda, tau, work, info)\
 **ZUNGL2** generates all or part of the unitary matrix Q from an LQ factorization determined by cgelqf (unblocked algorithm).

## Detailed Description

## Function Documentation

### subroutine cungl2 (integer m, integer n, integer k, complex, dimension( lda, \* ) a, integer lda, complex, dimension( \* ) tau, complex, dimension( \* ) work, integer info)

**CUNGL2** generates all or part of the unitary matrix Q from an LQ factorization determined by cgelqf (unblocked algorithm).

**Purpose:**

```
!>
!> CUNGL2 generates an m-by-n complex matrix Q with orthonormal rows,
!> which is defined as the first m rows of a product of k elementary
!> reflectors of order n
!>
!>       Q  =  H(k)**H . . . H(2)**H H(1)**H
!>
!> as returned by CGELQF.
!>
```

**Parameters**

*M*

```
!>          M is INTEGER
!>          The number of rows of the matrix Q. M >= 0.
!>
```

*N*

```
!>          N is INTEGER
!>          The number of columns of the matrix Q. N >= M.
!>
```

*K*

```
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines the
!>          matrix Q. M >= K >= 0.
!>
```

*A*

```
!>          A is COMPLEX array, dimension (LDA,N)
!>          On entry, the i-th row must contain the vector which defines
!>          the elementary reflector H(i), for i = 1,2,...,k, as returned
!>          by CGELQF in the first k rows of its array argument A.
!>          On exit, the m by n matrix Q.
!>
```

*LDA*

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

*TAU*

```
!>          TAU is COMPLEX array, dimension (K)
!>          TAU(i) must contain the scalar factor of the elementary
!>          reflector H(i), as returned by CGELQF.
!>
```

*WORK*

```
!>          WORK is COMPLEX array, dimension (M)
!>
```

*INFO*

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

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **112** of file **cungl2.f**.

### subroutine dorgl2 (integer m, integer n, integer k, double precision, dimension( lda, \* ) a, integer lda, double precision, dimension( \* ) tau, double precision, dimension( \* ) work, integer info)

**DORGL2**

**Purpose:**

```
!>
!> DORGL2 generates an m by n real matrix Q with orthonormal rows,
!> which is defined as the first m rows of a product of k elementary
!> reflectors of order n
!>
!>       Q  =  H(k) . . . H(2) H(1)
!>
!> as returned by DGELQF.
!>
```

**Parameters**

*M*

```
!>          M is INTEGER
!>          The number of rows of the matrix Q. M >= 0.
!>
```

*N*

```
!>          N is INTEGER
!>          The number of columns of the matrix Q. N >= M.
!>
```

*K*

```
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines the
!>          matrix Q. M >= K >= 0.
!>
```

*A*

```
!>          A is DOUBLE PRECISION array, dimension (LDA,N)
!>          On entry, the i-th row must contain the vector which defines
!>          the elementary reflector H(i), for i = 1,2,...,k, as returned
!>          by DGELQF in the first k rows of its array argument A.
!>          On exit, the m-by-n matrix Q.
!>
```

*LDA*

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

*TAU*

```
!>          TAU is DOUBLE PRECISION array, dimension (K)
!>          TAU(i) must contain the scalar factor of the elementary
!>          reflector H(i), as returned by DGELQF.
!>
```

*WORK*

```
!>          WORK is DOUBLE PRECISION array, dimension (M)
!>
```

*INFO*

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

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **112** of file **dorgl2.f**.

### subroutine sorgl2 (integer m, integer n, integer k, real, dimension( lda, \* ) a, integer lda, real, dimension( \* ) tau, real, dimension( \* ) work, integer info)

**SORGL2**

**Purpose:**

```
!>
!> SORGL2 generates an m by n real matrix Q with orthonormal rows,
!> which is defined as the first m rows of a product of k elementary
!> reflectors of order n
!>
!>       Q  =  H(k) . . . H(2) H(1)
!>
!> as returned by SGELQF.
!>
```

**Parameters**

*M*

```
!>          M is INTEGER
!>          The number of rows of the matrix Q. M >= 0.
!>
```

*N*

```
!>          N is INTEGER
!>          The number of columns of the matrix Q. N >= M.
!>
```

*K*

```
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines the
!>          matrix Q. M >= K >= 0.
!>
```

*A*

```
!>          A is REAL array, dimension (LDA,N)
!>          On entry, the i-th row must contain the vector which defines
!>          the elementary reflector H(i), for i = 1,2,...,k, as returned
!>          by SGELQF in the first k rows of its array argument A.
!>          On exit, the m-by-n matrix Q.
!>
```

*LDA*

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

*TAU*

```
!>          TAU is REAL array, dimension (K)
!>          TAU(i) must contain the scalar factor of the elementary
!>          reflector H(i), as returned by SGELQF.
!>
```

*WORK*

```
!>          WORK is REAL array, dimension (M)
!>
```

*INFO*

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

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **112** of file **sorgl2.f**.

### subroutine zungl2 (integer m, integer n, integer k, complex\*16, dimension( lda, \* ) a, integer lda, complex\*16, dimension( \* ) tau, complex\*16, dimension( \* ) work, integer info)

**ZUNGL2** generates all or part of the unitary matrix Q from an LQ factorization determined by cgelqf (unblocked algorithm).

**Purpose:**

```
!>
!> ZUNGL2 generates an m-by-n complex matrix Q with orthonormal rows,
!> which is defined as the first m rows of a product of k elementary
!> reflectors of order n
!>
!>       Q  =  H(k)**H . . . H(2)**H H(1)**H
!>
!> as returned by ZGELQF.
!>
```

**Parameters**

*M*

```
!>          M is INTEGER
!>          The number of rows of the matrix Q. M >= 0.
!>
```

*N*

```
!>          N is INTEGER
!>          The number of columns of the matrix Q. N >= M.
!>
```

*K*

```
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines the
!>          matrix Q. M >= K >= 0.
!>
```

*A*

```
!>          A is COMPLEX*16 array, dimension (LDA,N)
!>          On entry, the i-th row must contain the vector which defines
!>          the elementary reflector H(i), for i = 1,2,...,k, as returned
!>          by ZGELQF in the first k rows of its array argument A.
!>          On exit, the m by n matrix Q.
!>
```

*LDA*

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

*TAU*

```
!>          TAU is COMPLEX*16 array, dimension (K)
!>          TAU(i) must contain the scalar factor of the elementary
!>          reflector H(i), as returned by ZGELQF.
!>
```

*WORK*

```
!>          WORK is COMPLEX*16 array, dimension (M)
!>
```

*INFO*

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

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **112** of file **zungl2.f**.

## Author

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