SORGTSQR_ROW(3)

SORGTSQR_ROW(3)

okay so bestie, welcome to the Library Functions Manual ✨ this one is all about SORGTSQR_ROW, and it is giving “I make orthonormal columns out of SLATSQR’s cute little block format” 💅. no cap, we are keeping every single detail.

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NAME

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/sorgtsqr_row.f

SYNOPSIS

Functions/Subroutines

subroutine SORGTSQR_ROW (m, n, mb, nb, a, lda, t, ldt, work, lwork, info)

SORGTSQR_ROW

Function/Subroutine Documentation

subroutine SORGTSQR_ROW (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_ROW

Purpose

bestie, SORGTSQR_ROW generates an M-by-N real matrix Q_out with orthonormal columns from the output of SLATSQR 💖. These N orthonormal columns are the first N columns of a product of complex unitary matrices Q(k)_in of order M, which are returned by SLATSQR in a special format.

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

The input matrices Q(k)_in are stored in row and column blocks in A. See the documentation of SLATSQR for more details on the format of Q(k)_in, where each Q(k)_in is represented by block Householder transformations. This routine calls an auxiliary routine SLARFB_GETT, where the computation is performed on each individual block. The algorithm first sweeps NB-sized column blocks from the right to left starting in the bottom row block and continues to the top row block (hence _ROW in the routine name). This sweep is in reverse order of the order in which SLATSQR generates the output blocks. 🦋

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 used as input. 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). See SLATSQR for more details.

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 the 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. See SLATSQR for more details on the format of T.

LDT

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

WORK

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

LWORK

The dimension of the array WORK. LWORK >= NBLOCAL * MAX(NBLOCAL,(N-NBLOCAL)), where NBLOCAL=MIN(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.

bestie, LWORK = -1 is the lil “just tell me the size, don’t actually do the whole thing” mode ✨

INFO

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

if INFO = -i, something in argument town is illegal and the routine is side-eyeing you 💀

Author

• Univ. of Tennessee
• Univ. of California Berkeley
• Univ. of Colorado Denver
• NAG Ltd.

Contributors:

November 2020, Igor Kozachenko, Computer Science Division, University of California, Berkeley.

Definition at line 186 of file sorgtsqr_row.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

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k bye bestie 💖 this page is LAPACK Version 3.12.0, and the footer path is /home/abui...gtsqr_row.f(3) ✨👑