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man pages->IRIX man pages -> complib/sgeqlf (3)
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### Contents

```
SGEQLF(3F)							    SGEQLF(3F)

```

### NAME[Toc][Back]

```     SGEQLF - compute a	QL factorization of a real M-by-N matrix A
```

### SYNOPSIS[Toc][Back]

```     SUBROUTINE	SGEQLF(	M, N, A, LDA, TAU, WORK, LWORK,	INFO )

INTEGER	INFO, LDA, LWORK, M, N

REAL		A( LDA,	* ), TAU( * ), WORK( LWORK )
```

### PURPOSE[Toc][Back]

```     SGEQLF computes a QL factorization	of a real M-by-N matrix	A:  A =	Q * L.

```

### ARGUMENTS[Toc][Back]

```     M	     (input) INTEGER
The number	of rows	of the matrix A.  M >= 0.

N	     (input) INTEGER
The number	of columns of the matrix A.  N >= 0.

A	     (input/output) REAL array,	dimension (LDA,N)
On	entry, the M-by-N matrix A.  On	exit, if m >= n, the lower
triangle of the subarray A(m-n+1:m,1:n) contains the N-by-N lower
triangular	matrix L; if m <= n, the elements on and below the
(n-m)-th superdiagonal contain the	M-by-N lower trapezoidal
matrix L; the remaining elements, with the	array TAU, represent
the orthogonal matrix Q as	a product of elementary	reflectors
(see Further Details).  LDA     (input) INTEGER The leading
dimension of the array A.	LDA >= max(1,M).

TAU     (output) REAL array, dimension (min(M,N))
The scalar	factors	of the elementary reflectors (see Further
Details).

WORK    (workspace/output)	REAL array, dimension (LWORK)
On	exit, if INFO =	0, WORK(1) returns the optimal LWORK.

LWORK   (input) INTEGER
The dimension of the array	WORK.  LWORK >=	max(1,N).  For optimum
performance LWORK >= N*NB,	where NB is the	optimal	blocksize.

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value

FURTHER	DETAILS
The matrix	Q is represented as a product of elementary reflectors

Q = H(k) . . . H(2) H(1), where	k = min(m,n).

Each H(i) has the form

Page 1

SGEQLF(3F)							    SGEQLF(3F)

H(i) = I - tau * v * v'

where tau is a real scalar, and v is a real vector	with
v(m-k+i+1:m) = 0 and v(m-k+i) = 1;	v(1:m-k+i-1) is	stored on exit in
A(1:m-k+i-1,n-k+i), and tau in TAU(i).
SGEQLF(3F)							    SGEQLF(3F)

```

### NAME[Toc][Back]

```     SGEQLF - compute a	QL factorization of a real M-by-N matrix A
```

### SYNOPSIS[Toc][Back]

```     SUBROUTINE	SGEQLF(	M, N, A, LDA, TAU, WORK, LWORK,	INFO )

INTEGER	INFO, LDA, LWORK, M, N

REAL		A( LDA,	* ), TAU( * ), WORK( LWORK )
```

### PURPOSE[Toc][Back]

```     SGEQLF computes a QL factorization	of a real M-by-N matrix	A:  A =	Q * L.

```

### ARGUMENTS[Toc][Back]

```     M	     (input) INTEGER
The number	of rows	of the matrix A.  M >= 0.

N	     (input) INTEGER
The number	of columns of the matrix A.  N >= 0.

A	     (input/output) REAL array,	dimension (LDA,N)
On	entry, the M-by-N matrix A.  On	exit, if m >= n, the lower
triangle of the subarray A(m-n+1:m,1:n) contains the N-by-N lower
triangular	matrix L; if m <= n, the elements on and below the
(n-m)-th superdiagonal contain the	M-by-N lower trapezoidal
matrix L; the remaining elements, with the	array TAU, represent
the orthogonal matrix Q as	a product of elementary	reflectors
(see Further Details).  LDA     (input) INTEGER The leading
dimension of the array A.	LDA >= max(1,M).

TAU     (output) REAL array, dimension (min(M,N))
The scalar	factors	of the elementary reflectors (see Further
Details).

WORK    (workspace/output)	REAL array, dimension (LWORK)
On	exit, if INFO =	0, WORK(1) returns the optimal LWORK.

LWORK   (input) INTEGER
The dimension of the array	WORK.  LWORK >=	max(1,N).  For optimum
performance LWORK >= N*NB,	where NB is the	optimal	blocksize.

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value

FURTHER	DETAILS
The matrix	Q is represented as a product of elementary reflectors

Q = H(k) . . . H(2) H(1), where	k = min(m,n).

Each H(i) has the form

Page 1

SGEQLF(3F)							    SGEQLF(3F)

H(i) = I - tau * v * v'

where tau is a real scalar, and v is a real vector	with
v(m-k+i+1:m) = 0 and v(m-k+i) = 1;	v(1:m-k+i-1) is	stored on exit in
A(1:m-k+i-1,n-k+i), and tau in TAU(i).

PPPPaaaaggggeeee 2222```
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