dgeqrf - compute a QR factorization of a real M-by-N matrix A
SUBROUTINE DGEQRF( M, N, A, LDA, TAU, WORK, LDWORK, INFO) INTEGER M, N, LDA, LDWORK, INFO DOUBLE PRECISION A(LDA,*), TAU(*), WORK(*)
SUBROUTINE DGEQRF_64( M, N, A, LDA, TAU, WORK, LDWORK, INFO) INTEGER*8 M, N, LDA, LDWORK, INFO DOUBLE PRECISION A(LDA,*), TAU(*), WORK(*)
SUBROUTINE GEQRF( [M], [N], A, [LDA], TAU, [WORK], [LDWORK], [INFO]) INTEGER :: M, N, LDA, LDWORK, INFO REAL(8), DIMENSION(:) :: TAU, WORK REAL(8), DIMENSION(:,:) :: A
SUBROUTINE GEQRF_64( [M], [N], A, [LDA], TAU, [WORK], [LDWORK], * [INFO]) INTEGER(8) :: M, N, LDA, LDWORK, INFO REAL(8), DIMENSION(:) :: TAU, WORK REAL(8), DIMENSION(:,:) :: A
#include <sunperf.h>
void dgeqrf(int m, int n, double *a, int lda, double *tau, int *info);
void dgeqrf_64(long m, long n, double *a, long lda, double *tau, long *info);
dgeqrf computes a QR factorization of a real M-by-N matrix A: A = Q * R.
min(m,n)
elementary reflectors (see Further
Details).
WORK(1)
returns the optimal LDWORK.
If LDWORK = -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 LDWORK is issued by XERBLA.
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
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).