# sorgtsqr.f - Man Page

## Synopsis

### Functions/Subroutines

subroutine sorgtsqr (M, N, MB, NB, A, LDA, T, LDT, WORK, LWORK, INFO)
SORGTSQR

## Function/Subroutine Documentation

### subroutine sorgtsqr (integer M, integer N, integer MB, integer NB, real, dimension( lda, * ) A, integer LDA, real, dimension( ldt, * ) T, integer LDT, real, dimension( * ) WORK, integer LWORK, integer INFO)

SORGTSQR

Purpose:

``` SORGTSQR generates an M-by-N real matrix Q_out with orthonormal columns,
which are the first N columns of a product of real orthogonal
matrices of order M which are returned by SLATSQR

Q_out = first_N_columns_of( Q(1)_in * Q(2)_in * ... * Q(k)_in ).

See the documentation for SLATSQR.```
Parameters

M

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

N

```          N is INTEGER
The number of columns of the matrix A. M >= N >= 0.```

MB

```          MB is INTEGER
The row block size used by SLATSQR to return
arrays A and T. MB > N.
(Note that if MB > M, then M is used instead of MB
as the row block size).```

NB

```          NB is INTEGER
The column block size used by SLATSQR to return
arrays A and T. NB >= 1.
(Note that if NB > N, then N is used instead of NB
as the column block size).```

A

```          A is REAL array, dimension (LDA,N)

On entry:

The elements on and above the diagonal are not accessed.
The elements below the diagonal represent the unit
lower-trapezoidal blocked matrix V computed by SLATSQR
that defines the input matrices Q_in(k) (ones on the
diagonal are not stored) (same format as the output A
below the diagonal in SLATSQR).

On exit:

The array A contains an M-by-N orthonormal matrix Q_out,
i.e the columns of A are orthogonal unit vectors.```

LDA

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

T

```          T is REAL array,
dimension (LDT, N * NIRB)
where NIRB = Number_of_input_row_blocks
= MAX( 1, CEIL((M-N)/(MB-N)) )
Let NICB = Number_of_input_col_blocks
= CEIL(N/NB)

The upper-triangular block reflectors used to define the
input matrices Q_in(k), k=(1:NIRB*NICB). The block
reflectors are stored in compact form in NIRB block
reflector sequences. Each of NIRB block reflector sequences
is stored in a larger NB-by-N column block of T and consists
of NICB smaller NB-by-NB upper-triangular column blocks.
(same format as the output T in SLATSQR).```

LDT

```          LDT is INTEGER
The leading dimension of the array T.
LDT >= max(1,min(NB1,N)).```

WORK

```          (workspace) REAL array, dimension (MAX(2,LWORK))
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.```

LWORK

```          The dimension of the array WORK.  LWORK >= (M+NB)*N.
If LWORK = -1, then a workspace query is assumed.
The routine only calculates the optimal size of the WORK
array, returns this value as the first entry of the WORK
array, and no error message related to LWORK is issued
by XERBLA.```

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.

Contributors:

``` November 2019, Igor Kozachenko,
Computer Science Division,
University of California, Berkeley```

Definition at line 173 of file sorgtsqr.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page sorgtsqr(3) is an alias of sorgtsqr.f(3).

Thu Apr 1 2021 Version 3.9.1 LAPACK