---
name: "dlaror.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/dlaror.f"
---

# dlaror.f(3)

## NAME

TESTING/MATGEN/dlaror.f

## SYNOPSIS

### Functions/Subroutines

subroutine **dlaror** (side, init, m, n, a, lda, iseed, x, info)\
 **DLAROR**

## Function/Subroutine Documentation

### subroutine dlaror (character side, character init, integer m, integer n, double precision, dimension( lda, \* ) a, integer lda, integer, dimension( 4 ) iseed, double precision, dimension( \* ) x, integer info)

**DLAROR**

**Purpose:**

```
!>
!> DLAROR pre- or post-multiplies an M by N matrix A by a random
!> orthogonal matrix U, overwriting A.  A may optionally be initialized
!> to the identity matrix before multiplying by U.  U is generated using
!> the method of G.W. Stewart (SIAM J. Numer. Anal. 17, 1980, 403-409).
!>
```

**Parameters**

*SIDE*

```
!>          SIDE is CHARACTER*1
!>          Specifies whether A is multiplied on the left or right by U.
!>          = 'L':         Multiply A on the left (premultiply) by U
!>          = 'R':         Multiply A on the right (postmultiply) by U'
!>          = 'C' or 'T':  Multiply A on the left by U and the right
!>                          by U' (Here, U' means U-transpose.)
!>
```

*INIT*

```
!>          INIT is CHARACTER*1
!>          Specifies whether or not A should be initialized to the
!>          identity matrix.
!>          = 'I':  Initialize A to (a section of) the identity matrix
!>                   before applying U.
!>          = 'N':  No initialization.  Apply U to the input matrix A.
!>
!>          INIT = 'I' may be used to generate square or rectangular
!>          orthogonal matrices:
!>
!>          For M = N and SIDE = 'L' or 'R', the rows will be orthogonal
!>          to each other, as will the columns.
!>
!>          If M < N, SIDE = 'R' produces a dense matrix whose rows are
!>          orthogonal and whose columns are not, while SIDE = 'L'
!>          produces a matrix whose rows are orthogonal, and whose first
!>          M columns are orthogonal, and whose remaining columns are
!>          zero.
!>
!>          If M > N, SIDE = 'L' produces a dense matrix whose columns
!>          are orthogonal and whose rows are not, while SIDE = 'R'
!>          produces a matrix whose columns are orthogonal, and whose
!>          first M rows are orthogonal, and whose remaining rows are
!>          zero.
!>
```

*M*

```
!>          M is INTEGER
!>          The number of rows of A.
!>
```

*N*

```
!>          N is INTEGER
!>          The number of columns of A.
!>
```

*A*

```
!>          A is DOUBLE PRECISION array, dimension (LDA, N)
!>          On entry, the array A.
!>          On exit, overwritten by U A ( if SIDE = 'L' ),
!>           or by A U ( if SIDE = 'R' ),
!>           or by U A U' ( if SIDE = 'C' or 'T').
!>
```

*LDA*

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

*ISEED*

```
!>          ISEED is INTEGER array, dimension (4)
!>          On entry ISEED specifies the seed of the random number
!>          generator. The array elements should be between 0 and 4095;
!>          if not they will be reduced mod 4096.  Also, ISEED(4) must
!>          be odd.  The random number generator uses a linear
!>          congruential sequence limited to small integers, and so
!>          should produce machine independent random numbers. The
!>          values of ISEED are changed on exit, and can be used in the
!>          next call to DLAROR to continue the same random number
!>          sequence.
!>
```

*X*

```
!>          X is DOUBLE PRECISION array, dimension (3*MAX( M, N ))
!>          Workspace of length
!>              2*M + N if SIDE = 'L',
!>              2*N + M if SIDE = 'R',
!>              3*N     if SIDE = 'C' or 'T'.
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          An error flag.  It is set to:
!>          = 0:  normal return
!>          < 0:  if INFO = -k, the k-th argument had an illegal value
!>          = 1:  if the random numbers generated by DLARND are bad.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **145** of file **dlaror.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.