dgeqr2 (3p)

Name

dgeqr2 - computes the QR factorization of a general rectangular matrix using an unblocked algorithm.

Synopsis

SUBROUTINE DGEQR2(M, N, A, LDA, TAU, WORK, INFO)


INTEGER INFO, LDA, M, N

DOUBLE PRECISION A(LDA,*), TAU(*), WORK(*)


SUBROUTINE DGEQR2_64(M, N, A, LDA, TAU, WORK, INFO)


INTEGER*8 INFO, LDA, M, N

DOUBLE PRECISION A(LDA,*), TAU(*), WORK(*)


F95 INTERFACE
SUBROUTINE GEQR2(M, N, A, LDA, TAU, WORK, INFO)


INTEGER :: M, N, LDA, INFO

REAL(8), DIMENSION(:,:) :: A

REAL(8), DIMENSION(:) :: TAU, WORK


SUBROUTINE GEQR2_64(M, N, A, LDA, TAU, WORK, INFO)


INTEGER(8) :: M, N, LDA, INFO

REAL(8), DIMENSION(:,:) :: A

REAL(8), DIMENSION(:) :: TAU, WORK


C INTERFACE
#include <sunperf.h>

void dgeqr2 (int m, int n, double *a, int lda, double *tau, int *info);


void  dgeqr2_64 (long m, long n, double *a, long lda, double *tau, long
*info);

Description

Oracle Solaris Studio Performance Library                           dgeqr2(3P)



NAME
       dgeqr2  - computes the QR factorization of a general rectangular matrix
       using an unblocked algorithm.


SYNOPSIS
       SUBROUTINE DGEQR2(M, N, A, LDA, TAU, WORK, INFO)


       INTEGER INFO, LDA, M, N

       DOUBLE PRECISION A(LDA,*), TAU(*), WORK(*)


       SUBROUTINE DGEQR2_64(M, N, A, LDA, TAU, WORK, INFO)


       INTEGER*8 INFO, LDA, M, N

       DOUBLE PRECISION A(LDA,*), TAU(*), WORK(*)


   F95 INTERFACE
       SUBROUTINE GEQR2(M, N, A, LDA, TAU, WORK, INFO)


       INTEGER :: M, N, LDA, INFO

       REAL(8), DIMENSION(:,:) :: A

       REAL(8), DIMENSION(:) :: TAU, WORK


       SUBROUTINE GEQR2_64(M, N, A, LDA, TAU, WORK, INFO)


       INTEGER(8) :: M, N, LDA, INFO

       REAL(8), DIMENSION(:,:) :: A

       REAL(8), DIMENSION(:) :: TAU, WORK


   C INTERFACE
       #include <sunperf.h>

       void dgeqr2 (int m, int n, double *a, int lda, double *tau, int *info);


       void  dgeqr2_64 (long m, long n, double *a, long lda, double *tau, long
                 *info);


PURPOSE
       dgeqr2 computes a QR factorization of a real m by n matrix A: A=Q*R.


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


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


       A (input/output)
                 A is DOUBLE PRECISION 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)
                 LDA is INTEGER
                 The leading dimension of the array A.  LDA >= max(1,M).


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


       WORK (output)
                 WORK is DOUBLE PRECISION array, dimension (N)


       INFO (output)
                 INFO is 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**T
       where  tau is a complex scalar, and v is a complex 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).



                                  7 Nov 2015                        dgeqr2(3P)