---
name: "cungr2.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/cungr2.f"
---

# cungr2.f(3)

## NAME

SRC/cungr2.f

## SYNOPSIS

### Functions/Subroutines

subroutine **cungr2** (m, n, k, a, lda, tau, work, info)\
 **CUNGR2** generates all or part of the unitary matrix Q from an RQ factorization determined by cgerqf (unblocked algorithm).

## Function/Subroutine Documentation

### subroutine cungr2 (integer m, integer n, integer k, complex, dimension( lda, \* ) a, integer lda, complex, dimension( \* ) tau, complex, dimension( \* ) work, integer info)

**CUNGR2** generates all or part of the unitary matrix Q from an RQ factorization determined by cgerqf (unblocked algorithm).

**Purpose:**

```
!>
!> CUNGR2 generates an m by n complex matrix Q with orthonormal rows,
!> which is defined as the last m rows of a product of k elementary
!> reflectors of order n
!>
!>       Q  =  H(1)**H H(2)**H . . . H(k)**H
!>
!> as returned by CGERQF.
!>
```

**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 (m-k+i)-th row must contain the vector which
!>          defines the elementary reflector H(i), for i = 1,2,...,k, as
!>          returned by CGERQF in the last 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 CGERQF.
!>
```

*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 **113** of file **cungr2.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.