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man pages->IRIX man pages -> complib/sgeqr2 (3)
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### Contents

```
SGEQR2(3F)							    SGEQR2(3F)

```

### NAME[Toc][Back]

```     SGEQR2 - compute a	QR factorization of a real m by	n matrix A
```

### SYNOPSIS[Toc][Back]

```     SUBROUTINE	SGEQR2(	M, N, A, LDA, TAU, WORK, INFO )

INTEGER	INFO, LDA, M, N

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

### PURPOSE[Toc][Back]

```     SGEQR2 computes a QR factorization	of a real m by n matrix	A:  A =	Q * R.

```

### 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, the elements on and
above the diagonal	of the array contain the min(m,n) by n upper
trapezoidal matrix	R (R is	upper triangular if m >= n); the
elements below the	diagonal, 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) REAL array, dimension (N)

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

Each H(i) has the form

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

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

Page 1

SGEQR2(3F)							    SGEQR2(3F)
SGEQR2(3F)							    SGEQR2(3F)

```

### NAME[Toc][Back]

```     SGEQR2 - compute a	QR factorization of a real m by	n matrix A
```

### SYNOPSIS[Toc][Back]

```     SUBROUTINE	SGEQR2(	M, N, A, LDA, TAU, WORK, INFO )

INTEGER	INFO, LDA, M, N

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

### PURPOSE[Toc][Back]

```     SGEQR2 computes a QR factorization	of a real m by n matrix	A:  A =	Q * R.

```

### 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, the elements on and
above the diagonal	of the array contain the min(m,n) by n upper
trapezoidal matrix	R (R is	upper triangular if m >= n); the
elements below the	diagonal, 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) REAL array, dimension (N)

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

Each H(i) has the form

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

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

Page 1

SGEQR2(3F)							    SGEQR2(3F)

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