---
name: "gemqrt"
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/gemqrt"
---

# gemqrt(3)

gemqrt: multiply by Q from geqrt

## NAME

gemqrt - gemqrt: multiply by Q from geqrt

## SYNOPSIS

### Functions

subroutine **cgemqrt** (side, trans, m, n, k, nb, v, ldv, t, ldt, c, ldc, work, info)\
 **CGEMQRT**  subroutine **dgemqrt** (side, trans, m, n, k, nb, v, ldv, t, ldt, c, ldc, work, info)\
 **DGEMQRT**  subroutine **sgemqrt** (side, trans, m, n, k, nb, v, ldv, t, ldt, c, ldc, work, info)\
 **SGEMQRT**  subroutine **zgemqrt** (side, trans, m, n, k, nb, v, ldv, t, ldt, c, ldc, work, info)\
 **ZGEMQRT**

## Detailed Description

## Function Documentation

### subroutine cgemqrt (character side, character trans, integer m, integer n, integer k, integer nb, complex, dimension( ldv, \* ) v, integer ldv, complex, dimension( ldt, \* ) t, integer ldt, complex, dimension( ldc, \* ) c, integer ldc, complex, dimension( \* ) work, integer info)

**CGEMQRT**

**Purpose:**

```
!>
!> CGEMQRT overwrites the general complex M-by-N matrix C with
!>
!>                 SIDE = 'L'     SIDE = 'R'
!> TRANS = 'N':      Q C            C Q
!> TRANS = 'C':    Q**H C            C Q**H
!>
!> where Q is a complex orthogonal matrix defined as the product of K
!> elementary reflectors:
!>
!>       Q = H(1) H(2) . . . H(K) = I - V T V**H
!>
!> generated using the compact WY representation as returned by CGEQRT.
!>
!> Q is of order M if SIDE = 'L' and of order N  if SIDE = 'R'.
!>
```

**Parameters**

*SIDE*

```
!>          SIDE is CHARACTER*1
!>          = 'L': apply Q or Q**H from the Left;
!>          = 'R': apply Q or Q**H from the Right.
!>
```

*TRANS*

```
!>          TRANS is CHARACTER*1
!>          = 'N':  No transpose, apply Q;
!>          = 'C':  Conjugate transpose, apply Q**H.
!>
```

*M*

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

*N*

```
!>          N is INTEGER
!>          The number of columns of the matrix C. N >= 0.
!>
```

*K*

```
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines
!>          the matrix Q.
!>          If SIDE = 'L', M >= K >= 0;
!>          if SIDE = 'R', N >= K >= 0.
!>
```

*NB*

```
!>          NB is INTEGER
!>          The block size used for the storage of T.  K >= NB >= 1.
!>          This must be the same value of NB used to generate T
!>          in CGEQRT.
!>
```

*V*

```
!>          V is COMPLEX array, dimension (LDV,K)
!>          The i-th column must contain the vector which defines the
!>          elementary reflector H(i), for i = 1,2,...,k, as returned by
!>          CGEQRT in the first K columns of its array argument A.
!>
```

*LDV*

```
!>          LDV is INTEGER
!>          The leading dimension of the array V.
!>          If SIDE = 'L', LDA >= max(1,M);
!>          if SIDE = 'R', LDA >= max(1,N).
!>
```

*T*

```
!>          T is COMPLEX array, dimension (LDT,K)
!>          The upper triangular factors of the block reflectors
!>          as returned by CGEQRT, stored as a NB-by-N matrix.
!>
```

*LDT*

```
!>          LDT is INTEGER
!>          The leading dimension of the array T.  LDT >= NB.
!>
```

*C*

```
!>          C is COMPLEX array, dimension (LDC,N)
!>          On entry, the M-by-N matrix C.
!>          On exit, C is overwritten by Q C, Q**H C, C Q**H or C Q.
!>
```

*LDC*

```
!>          LDC is INTEGER
!>          The leading dimension of the array C. LDC >= max(1,M).
!>
```

*WORK*

```
!>          WORK is COMPLEX array. The dimension of WORK is
!>           N*NB if SIDE = 'L', or  M*NB if SIDE = 'R'.
!>
```

*INFO*

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

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **166** of file **cgemqrt.f**.

### subroutine dgemqrt (character side, character trans, integer m, integer n, integer k, integer nb, double precision, dimension( ldv, \* ) v, integer ldv, double precision, dimension( ldt, \* ) t, integer ldt, double precision, dimension( ldc, \* ) c, integer ldc, double precision, dimension( \* ) work, integer info)

**DGEMQRT**

**Purpose:**

```
!>
!> DGEMQRT overwrites the general real M-by-N matrix C with
!>
!>                 SIDE = 'L'     SIDE = 'R'
!> TRANS = 'N':      Q C            C Q
!> TRANS = 'T':   Q**T C            C Q**T
!>
!> where Q is a real orthogonal matrix defined as the product of K
!> elementary reflectors:
!>
!>       Q = H(1) H(2) . . . H(K) = I - V T V**T
!>
!> generated using the compact WY representation as returned by DGEQRT.
!>
!> Q is of order M if SIDE = 'L' and of order N  if SIDE = 'R'.
!>
```

**Parameters**

*SIDE*

```
!>          SIDE is CHARACTER*1
!>          = 'L': apply Q or Q**T from the Left;
!>          = 'R': apply Q or Q**T from the Right.
!>
```

*TRANS*

```
!>          TRANS is CHARACTER*1
!>          = 'N':  No transpose, apply Q;
!>          = 'C':  Transpose, apply Q**T.
!>
```

*M*

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

*N*

```
!>          N is INTEGER
!>          The number of columns of the matrix C. N >= 0.
!>
```

*K*

```
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines
!>          the matrix Q.
!>          If SIDE = 'L', M >= K >= 0;
!>          if SIDE = 'R', N >= K >= 0.
!>
```

*NB*

```
!>          NB is INTEGER
!>          The block size used for the storage of T.  K >= NB >= 1.
!>          This must be the same value of NB used to generate T
!>          in DGEQRT.
!>
```

*V*

```
!>          V is DOUBLE PRECISION array, dimension (LDV,K)
!>          The i-th column must contain the vector which defines the
!>          elementary reflector H(i), for i = 1,2,...,k, as returned by
!>          DGEQRT in the first K columns of its array argument A.
!>
```

*LDV*

```
!>          LDV is INTEGER
!>          The leading dimension of the array V.
!>          If SIDE = 'L', LDA >= max(1,M);
!>          if SIDE = 'R', LDA >= max(1,N).
!>
```

*T*

```
!>          T is DOUBLE PRECISION array, dimension (LDT,K)
!>          The upper triangular factors of the block reflectors
!>          as returned by DGEQRT, stored as a NB-by-N matrix.
!>
```

*LDT*

```
!>          LDT is INTEGER
!>          The leading dimension of the array T.  LDT >= NB.
!>
```

*C*

```
!>          C is DOUBLE PRECISION array, dimension (LDC,N)
!>          On entry, the M-by-N matrix C.
!>          On exit, C is overwritten by Q C, Q**T C, C Q**T or C Q.
!>
```

*LDC*

```
!>          LDC is INTEGER
!>          The leading dimension of the array C. LDC >= max(1,M).
!>
```

*WORK*

```
!>          WORK is DOUBLE PRECISION array. The dimension of
!>          WORK is N*NB if SIDE = 'L', or  M*NB if SIDE = 'R'.
!>
```

*INFO*

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

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **166** of file **dgemqrt.f**.

### subroutine sgemqrt (character side, character trans, integer m, integer n, integer k, integer nb, real, dimension( ldv, \* ) v, integer ldv, real, dimension( ldt, \* ) t, integer ldt, real, dimension( ldc, \* ) c, integer ldc, real, dimension( \* ) work, integer info)

**SGEMQRT**

**Purpose:**

```
!>
!> SGEMQRT overwrites the general real M-by-N matrix C with
!>
!>                 SIDE = 'L'     SIDE = 'R'
!> TRANS = 'N':      Q C            C Q
!> TRANS = 'T':   Q**T C            C Q**T
!>
!> where Q is a real orthogonal matrix defined as the product of K
!> elementary reflectors:
!>
!>       Q = H(1) H(2) . . . H(K) = I - V T V**T
!>
!> generated using the compact WY representation as returned by SGEQRT.
!>
!> Q is of order M if SIDE = 'L' and of order N  if SIDE = 'R'.
!>
```

**Parameters**

*SIDE*

```
!>          SIDE is CHARACTER*1
!>          = 'L': apply Q or Q**T from the Left;
!>          = 'R': apply Q or Q**T from the Right.
!>
```

*TRANS*

```
!>          TRANS is CHARACTER*1
!>          = 'N':  No transpose, apply Q;
!>          = 'T':  Transpose, apply Q**T.
!>
```

*M*

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

*N*

```
!>          N is INTEGER
!>          The number of columns of the matrix C. N >= 0.
!>
```

*K*

```
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines
!>          the matrix Q.
!>          If SIDE = 'L', M >= K >= 0;
!>          if SIDE = 'R', N >= K >= 0.
!>
```

*NB*

```
!>          NB is INTEGER
!>          The block size used for the storage of T.  K >= NB >= 1.
!>          This must be the same value of NB used to generate T
!>          in SGEQRT.
!>
```

*V*

```
!>          V is REAL array, dimension (LDV,K)
!>          The i-th column must contain the vector which defines the
!>          elementary reflector H(i), for i = 1,2,...,k, as returned by
!>          SGEQRT in the first K columns of its array argument A.
!>
```

*LDV*

```
!>          LDV is INTEGER
!>          The leading dimension of the array V.
!>          If SIDE = 'L', LDA >= max(1,M);
!>          if SIDE = 'R', LDA >= max(1,N).
!>
```

*T*

```
!>          T is REAL array, dimension (LDT,K)
!>          The upper triangular factors of the block reflectors
!>          as returned by SGEQRT, stored as a NB-by-N matrix.
!>
```

*LDT*

```
!>          LDT is INTEGER
!>          The leading dimension of the array T.  LDT >= NB.
!>
```

*C*

```
!>          C is REAL array, dimension (LDC,N)
!>          On entry, the M-by-N matrix C.
!>          On exit, C is overwritten by Q C, Q**T C, C Q**T or C Q.
!>
```

*LDC*

```
!>          LDC is INTEGER
!>          The leading dimension of the array C. LDC >= max(1,M).
!>
```

*WORK*

```
!>          WORK is REAL array. The dimension of WORK is
!>           N*NB if SIDE = 'L', or  M*NB if SIDE = 'R'.
!>
```

*INFO*

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

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **166** of file **sgemqrt.f**.

### subroutine zgemqrt (character side, character trans, integer m, integer n, integer k, integer nb, complex\*16, dimension( ldv, \* ) v, integer ldv, complex\*16, dimension( ldt, \* ) t, integer ldt, complex\*16, dimension( ldc, \* ) c, integer ldc, complex\*16, dimension( \* ) work, integer info)

**ZGEMQRT**

**Purpose:**

```
!>
!> ZGEMQRT overwrites the general complex M-by-N matrix C with
!>
!>                 SIDE = 'L'     SIDE = 'R'
!> TRANS = 'N':      Q C            C Q
!> TRANS = 'C':    Q**H C            C Q**H
!>
!> where Q is a complex orthogonal matrix defined as the product of K
!> elementary reflectors:
!>
!>       Q = H(1) H(2) . . . H(K) = I - V T V**H
!>
!> generated using the compact WY representation as returned by ZGEQRT.
!>
!> Q is of order M if SIDE = 'L' and of order N  if SIDE = 'R'.
!>
```

**Parameters**

*SIDE*

```
!>          SIDE is CHARACTER*1
!>          = 'L': apply Q or Q**H from the Left;
!>          = 'R': apply Q or Q**H from the Right.
!>
```

*TRANS*

```
!>          TRANS is CHARACTER*1
!>          = 'N':  No transpose, apply Q;
!>          = 'C':  Conjugate transpose, apply Q**H.
!>
```

*M*

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

*N*

```
!>          N is INTEGER
!>          The number of columns of the matrix C. N >= 0.
!>
```

*K*

```
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines
!>          the matrix Q.
!>          If SIDE = 'L', M >= K >= 0;
!>          if SIDE = 'R', N >= K >= 0.
!>
```

*NB*

```
!>          NB is INTEGER
!>          The block size used for the storage of T.  K >= NB >= 1.
!>          This must be the same value of NB used to generate T
!>          in ZGEQRT.
!>
```

*V*

```
!>          V is COMPLEX*16 array, dimension (LDV,K)
!>          The i-th column must contain the vector which defines the
!>          elementary reflector H(i), for i = 1,2,...,k, as returned by
!>          ZGEQRT in the first K columns of its array argument A.
!>
```

*LDV*

```
!>          LDV is INTEGER
!>          The leading dimension of the array V.
!>          If SIDE = 'L', LDA >= max(1,M);
!>          if SIDE = 'R', LDA >= max(1,N).
!>
```

*T*

```
!>          T is COMPLEX*16 array, dimension (LDT,K)
!>          The upper triangular factors of the block reflectors
!>          as returned by ZGEQRT, stored as a NB-by-N matrix.
!>
```

*LDT*

```
!>          LDT is INTEGER
!>          The leading dimension of the array T.  LDT >= NB.
!>
```

*C*

```
!>          C is COMPLEX*16 array, dimension (LDC,N)
!>          On entry, the M-by-N matrix C.
!>          On exit, C is overwritten by Q C, Q**H C, C Q**H or C Q.
!>
```

*LDC*

```
!>          LDC is INTEGER
!>          The leading dimension of the array C. LDC >= max(1,M).
!>
```

*WORK*

```
!>          WORK is COMPLEX*16 array. The dimension of WORK is
!>           N*NB if SIDE = 'L', or  M*NB if SIDE = 'R'.
!>
```

*INFO*

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

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **166** of file **zgemqrt.f**.

## Author

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