DGBBRD(3F)DGBBRD(3F)NAME
DGBBRD - reduce a real general m-by-n band matrix A to upper bidiagonal
form B by an orthogonal transformation
SYNOPSIS
SUBROUTINE DGBBRD( VECT, M, N, NCC, KL, KU, AB, LDAB, D, E, Q, LDQ, PT,
LDPT, C, LDC, WORK, INFO )
CHARACTER VECT
INTEGER INFO, KL, KU, LDAB, LDC, LDPT, LDQ, M, N, NCC
DOUBLE PRECISION AB( LDAB, * ), C( LDC, * ), D( * ), E( * ),
PT( LDPT, * ), Q( LDQ, * ), WORK( * )
PURPOSE
DGBBRD reduces a real general m-by-n band matrix A to upper bidiagonal
form B by an orthogonal transformation: Q' * A * P = B.
The routine computes B, and optionally forms Q or P', or computes Q'*C
for a given matrix C.
ARGUMENTS
VECT (input) CHARACTER*1
Specifies whether or not the matrices Q and P' are to be formed.
= 'N': do not form Q or P';
= 'Q': form Q only;
= 'P': form P' only;
= 'B': form both.
M (input) INTEGER
The number of rows of the matrix A. M >= 0.
N (input) INTEGER
The number of columns of the matrix A. N >= 0.
NCC (input) INTEGER
The number of columns of the matrix C. NCC >= 0.
KL (input) INTEGER
The number of subdiagonals of the matrix A. KL >= 0.
KU (input) INTEGER
The number of superdiagonals of the matrix A. KU >= 0.
AB (input/output) DOUBLE PRECISION array, dimension (LDAB,N)
On entry, the m-by-n band matrix A, stored in rows 1 to KL+KU+1.
The j-th column of A is stored in the j-th column of the array AB
as follows: AB(ku+1+i-j,j) = A(i,j) for max(1,j-
ku)<=i<=min(m,j+kl). On exit, A is overwritten by values
generated during the reduction.
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DGBBRD(3F)DGBBRD(3F)
LDAB (input) INTEGER
The leading dimension of the array A. LDAB >= KL+KU+1.
D (output) DOUBLE PRECISION array, dimension (min(M,N))
The diagonal elements of the bidiagonal matrix B.
E (output) DOUBLE PRECISION array, dimension (min(M,N)-1)
The superdiagonal elements of the bidiagonal matrix B.
Q (output) DOUBLE PRECISION array, dimension (LDQ,M)
If VECT = 'Q' or 'B', the m-by-m orthogonal matrix Q. If VECT =
'N' or 'P', the array Q is not referenced.
LDQ (input) INTEGER
The leading dimension of the array Q. LDQ >= max(1,M) if VECT =
'Q' or 'B'; LDQ >= 1 otherwise.
PT (output) DOUBLE PRECISION array, dimension (LDPT,N)
If VECT = 'P' or 'B', the n-by-n orthogonal matrix P'. If VECT =
'N' or 'Q', the array PT is not referenced.
LDPT (input) INTEGER
The leading dimension of the array PT. LDPT >= max(1,N) if VECT
= 'P' or 'B'; LDPT >= 1 otherwise.
C (input/output) DOUBLE PRECISION array, dimension (LDC,NCC)
On entry, an m-by-ncc matrix C. On exit, C is overwritten by
Q'*C. C is not referenced if NCC = 0.
LDC (input) INTEGER
The leading dimension of the array C. LDC >= max(1,M) if NCC >
0; LDC >= 1 if NCC = 0.
WORK (workspace) DOUBLE PRECISION array, dimension (2*max(M,N))
INFO (output) INTEGER
= 0: successful exit.
< 0: if INFO = -i, the i-th argument had an illegal value.
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