# zgetsqrhrt.f - Man Page

## Synopsis

### Functions/Subroutines

subroutine **zgetsqrhrt** (M, **N**, MB1, NB1, NB2, A, **LDA**, T, LDT, WORK, LWORK, INFO)**ZGETSQRHRT**

## Function/Subroutine Documentation

### subroutine zgetsqrhrt (integer M, integer N, integer MB1, integer NB1, integer NB2, complex*16, dimension( lda, * ) A, integer LDA, complex*16, dimension( ldt, * ) T, integer LDT, complex*16, dimension( * ) WORK, integer LWORK, integer INFO)

**ZGETSQRHRT**

**Purpose:**

ZGETSQRHRT computes a NB2-sized column blocked QR-factorization of a complex M-by-N matrix A with M >= N, A = Q * R. The routine uses internally a NB1-sized column blocked and MB1-sized row blocked TSQR-factorization and perfors the reconstruction of the Householder vectors from the TSQR output. The routine also converts the R_tsqr factor from the TSQR-factorization output into the R factor that corresponds to the Householder QR-factorization, A = Q_tsqr * R_tsqr = Q * R. The output Q and R factors are stored in the same format as in ZGEQRT (Q is in blocked compact WY-representation). See the documentation of ZGEQRT for more details on the format.

**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.

*MB1*MB1 is INTEGER The row block size to be used in the blocked TSQR. MB1 > N.

*NB1*NB1 is INTEGER The column block size to be used in the blocked TSQR. N >= NB1 >= 1.

*NB2*NB2 is INTEGER The block size to be used in the blocked QR that is output. NB2 >= 1.

*A*A is COMPLEX*16 array, dimension (LDA,N) On entry: an M-by-N matrix A. On exit: a) the elements on and above the diagonal of the array contain the N-by-N upper-triangular matrix R corresponding to the Householder QR; b) the elements below the diagonal represent Q by the columns of blocked V (compact WY-representation).

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

*T*T is COMPLEX*16 array, dimension (LDT,N)) The upper triangular block reflectors stored in compact form as a sequence of upper triangular blocks.

*LDT*LDT is INTEGER The leading dimension of the array T. LDT >= NB2.

*WORK*(workspace) COMPLEX*16 array, dimension (MAX(1,LWORK)) On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

*LWORK*The dimension of the array WORK. LWORK >= MAX( LWT + LW1, MAX( LWT+N*N+LW2, LWT+N*N+N ) ), where NUM_ALL_ROW_BLOCKS = CEIL((M-N)/(MB1-N)), NB1LOCAL = MIN(NB1,N). LWT = NUM_ALL_ROW_BLOCKS * N * NB1LOCAL, LW1 = NB1LOCAL * N, LW2 = NB1LOCAL * MAX( NB1LOCAL, ( N - NB1LOCAL ) ), 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 2020, Igor Kozachenko, Computer Science Division, University of California, Berkeley

Definition at line 177 of file zgetsqrhrt.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Thu Apr 1 2021 Version 3.9.1 LAPACK