zgebrd - reduce a general complex M-by-N matrix A to upper or lower bidiagonal form B by a unitary transformation
SUBROUTINE ZGEBRD( M, N, A, LDA, D, E, TAUQ, TAUP, WORK, LWORK, * INFO) DOUBLE COMPLEX A(LDA,*), TAUQ(*), TAUP(*), WORK(*) INTEGER M, N, LDA, LWORK, INFO DOUBLE PRECISION D(*), E(*)
SUBROUTINE ZGEBRD_64( M, N, A, LDA, D, E, TAUQ, TAUP, WORK, LWORK, * INFO) DOUBLE COMPLEX A(LDA,*), TAUQ(*), TAUP(*), WORK(*) INTEGER*8 M, N, LDA, LWORK, INFO DOUBLE PRECISION D(*), E(*)
SUBROUTINE GEBRD( [M], [N], A, [LDA], D, E, TAUQ, TAUP, [WORK], * [LWORK], [INFO]) COMPLEX(8), DIMENSION(:) :: TAUQ, TAUP, WORK COMPLEX(8), DIMENSION(:,:) :: A INTEGER :: M, N, LDA, LWORK, INFO REAL(8), DIMENSION(:) :: D, E
SUBROUTINE GEBRD_64( [M], [N], A, [LDA], D, E, TAUQ, TAUP, [WORK], * [LWORK], [INFO]) COMPLEX(8), DIMENSION(:) :: TAUQ, TAUP, WORK COMPLEX(8), DIMENSION(:,:) :: A INTEGER(8) :: M, N, LDA, LWORK, INFO REAL(8), DIMENSION(:) :: D, E
#include <sunperf.h>
void zgebrd(int m, int n, doublecomplex *a, int lda, double *d, double *e, doublecomplex *tauq, doublecomplex *taup, int *info);
void zgebrd_64(long m, long n, doublecomplex *a, long lda, double *d, double *e, doublecomplex *tauq, doublecomplex *taup, long *info);
zgebrd reduces a general complex M-by-N matrix A to upper or lower bidiagonal form B by a unitary transformation: Q**H * A * P = B.
If m >= n, B is upper bidiagonal; if m < n, B is lower bidiagonal.
D(i)
= A(i,i).
E(i)
= A(i,i+1)
for i = 1,2,...,n-1;
if m < n, E(i)
= A(i+1,i)
for i = 1,2,...,m-1.
WORK(1)
returns the optimal LWORK.
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.
= 0: successful exit.
< 0: if INFO = -i, the i-th argument had an illegal value.
The matrices Q and P are represented as products of elementary reflectors:
If m > = n,
Q = H(1) H(2) . . . H(n) and P = G(1) G(2) . . . G(n-1)
Each H(i)
and G(i)
has the form:
H(i) = I - tauq * v * v' and G(i) = I - taup * u * u'
where tauq and taup are complex scalars, and v and u are complex
vectors; v(1:i-1)
= 0, v(i)
= 1, and v(i+1:m)
is stored on exit in
A(i+1:m,i); u(1:i)
= 0, u(i+1)
= 1, and u(i+2:n)
is stored on exit in
A(i,i+2:n); tauq is stored in TAUQ(i)
and taup in TAUP(i).
If m < n,
Q = H(1) H(2) . . . H(m-1) and P = G(1) G(2) . . . G(m)
Each H(i)
and G(i)
has the form:
H(i) = I - tauq * v * v' and G(i) = I - taup * u * u'
where tauq and taup are complex scalars, and v and u are complex
vectors; v(1:i)
= 0, v(i+1)
= 1, and v(i+2:m)
is stored on exit in
A(i+2:m,i); u(1:i-1)
= 0, u(i)
= 1, and u(i+1:n)
is stored on exit in
A(i,i+1:n); tauq is stored in TAUQ(i)
and taup in TAUP(i).
The contents of A on exit are illustrated by the following examples:
m = 6 and n = 5 (m > n): m = 5 and n = 6 (m < n):
( d e u1 u1 u1 ) ( d u1 u1 u1 u1 u1 ) ( v1 d e u2 u2 ) ( e d u2 u2 u2 u2 ) ( v1 v2 d e u3 ) ( v1 e d u3 u3 u3 ) ( v1 v2 v3 d e ) ( v1 v2 e d u4 u4 ) ( v1 v2 v3 v4 d ) ( v1 v2 v3 e d u5 ) ( v1 v2 v3 v4 v5 )
where d and e denote diagonal and off-diagonal elements of B, vi denotes an element of the vector defining H(i), and ui an element of the vector defining G(i).