NAME

sgbbrd - reduce a real general m-by-n band matrix A to upper bidiagonal form B by an orthogonal transformation

SYNOPSIS

SUBROUTINE SGBBRD(
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

REAL AB( LDAB, ∗ ), C( LDC, ∗ ), D( ∗ ), E( ∗ ), PT( LDPT, ∗ ), Q( LDQ, ∗ ), WORK( ∗ )

PURPOSE

SGBBRD 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) REAL 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.

LDAB    (input) INTEGER
The leading dimension of the array A. LDAB >= KL+KU+1.

D       (output) REAL array, dimension (min(M,N))
The diagonal elements of the bidiagonal matrix B.

E       (output) REAL array, dimension (min(M,N)-1)
The superdiagonal elements of the bidiagonal matrix B.

Q       (output) REAL 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) REAL 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) REAL 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) REAL array, dimension (2∗max(M,N))

INFO    (output) INTEGER
= 0:  successful exit.
< 0:  if INFO = -i, the i-th argument had an illegal value.

SunSoft, Inc.  —  Last change: 27 Jun 1995