
dsbtrd.f(3) LAPACK dsbtrd.f(3)
NAME
dsbtrd.f 
SYNOPSIS
Functions/Subroutines
subroutine dsbtrd (VECT, UPLO, N, KD, AB, LDAB, D, E, Q, LDQ, WORK, INFO)
DSBTRD
Function/Subroutine Documentation
subroutine dsbtrd (characterVECT, characterUPLO, integerN, integerKD, double precision,
dimension( ldab, * )AB, integerLDAB, double precision, dimension( * )D, double precision,
dimension( * )E, double precision, dimension( ldq, * )Q, integerLDQ, double precision,
dimension( * )WORK, integerINFO)
DSBTRD
Purpose:
DSBTRD reduces a real symmetric band matrix A to symmetric
tridiagonal form T by an orthogonal similarity transformation:
Q**T * A * Q = T.
Parameters:
VECT
VECT is CHARACTER*1
= 'N': do not form Q;
= 'V': form Q;
= 'U': update a matrix X, by forming X*Q.
UPLO
UPLO is CHARACTER*1
= 'U': Upper triangle of A is stored;
= 'L': Lower triangle of A is stored.
N
N is INTEGER
The order of the matrix A. N >= 0.
KD
KD is INTEGER
The number of superdiagonals of the matrix A if UPLO = 'U',
or the number of subdiagonals if UPLO = 'L'. KD >= 0.
AB
AB is DOUBLE PRECISION array, dimension (LDAB,N)
On entry, the upper or lower triangle of the symmetric band
matrix A, stored in the first KD+1 rows of the array. The
jth column of A is stored in the jth column of the array AB
as follows:
if UPLO = 'U', AB(kd+1+ij,j) = A(i,j) for max(1,jkd)<=i<=j;
if UPLO = 'L', AB(1+ij,j) = A(i,j) for j<=i<=min(n,j+kd).
On exit, the diagonal elements of AB are overwritten by the
diagonal elements of the tridiagonal matrix T; if KD > 0, the
elements on the first superdiagonal (if UPLO = 'U') or the
first subdiagonal (if UPLO = 'L') are overwritten by the
offdiagonal elements of T; the rest of AB is overwritten by
values generated during the reduction.
LDAB
LDAB is INTEGER
The leading dimension of the array AB. LDAB >= KD+1.
D
D is DOUBLE PRECISION array, dimension (N)
The diagonal elements of the tridiagonal matrix T.
E
E is DOUBLE PRECISION array, dimension (N1)
The offdiagonal elements of the tridiagonal matrix T:
E(i) = T(i,i+1) if UPLO = 'U'; E(i) = T(i+1,i) if UPLO = 'L'.
Q
Q is DOUBLE PRECISION array, dimension (LDQ,N)
On entry, if VECT = 'U', then Q must contain an NbyN
matrix X; if VECT = 'N' or 'V', then Q need not be set.
On exit:
if VECT = 'V', Q contains the NbyN orthogonal matrix Q;
if VECT = 'U', Q contains the product X*Q;
if VECT = 'N', the array Q is not referenced.
LDQ
LDQ is INTEGER
The leading dimension of the array Q.
LDQ >= 1, and LDQ >= N if VECT = 'V' or 'U'.
WORK
WORK is DOUBLE PRECISION array, dimension (N)
INFO
INFO is INTEGER
= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Further Details:
Modified by Linda Kaufman, Bell Labs.
Definition at line 163 of file dsbtrd.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dsbtrd.f(3) 
