
SSBGV(l) ) SSBGV(l)
NAME
SSBGV  compute all the eigenvalues, and optionally, the eigenvectors of a real general
ized symmetricdefinite banded eigenproblem, of the form A*x=(lambda)*B*x
SYNOPSIS
SUBROUTINE SSBGV( JOBZ, UPLO, N, KA, KB, AB, LDAB, BB, LDBB, W, Z, LDZ, WORK, INFO )
CHARACTER JOBZ, UPLO
INTEGER INFO, KA, KB, LDAB, LDBB, LDZ, N
REAL AB( LDAB, * ), BB( LDBB, * ), W( * ), WORK( * ), Z( LDZ, * )
PURPOSE
SSBGV computes all the eigenvalues, and optionally, the eigenvectors of a real generalized
symmetricdefinite banded eigenproblem, of the form A*x=(lambda)*B*x. Here A and B are
assumed to be symmetric and banded, and B is also positive definite.
ARGUMENTS
JOBZ (input) CHARACTER*1
= 'N': Compute eigenvalues only;
= 'V': Compute eigenvalues and eigenvectors.
UPLO (input) CHARACTER*1
= 'U': Upper triangles of A and B are stored;
= 'L': Lower triangles of A and B are stored.
N (input) INTEGER
The order of the matrices A and B. N >= 0.
KA (input) INTEGER
The number of superdiagonals of the matrix A if UPLO = 'U', or the number of sub
diagonals if UPLO = 'L'. KA >= 0.
KB (input) INTEGER
The number of superdiagonals of the matrix B if UPLO = 'U', or the number of sub
diagonals if UPLO = 'L'. KB >= 0.
AB (input/output) REAL array, dimension (LDAB, N)
On entry, the upper or lower triangle of the symmetric band matrix A, stored in
the first ka+1 rows of the array. The jth column of A is stored in the jth col
umn of the array AB as follows: if UPLO = 'U', AB(ka+1+ij,j) = A(i,j) for
max(1,jka)<=i<=j; if UPLO = 'L', AB(1+ij,j) = A(i,j) for j<=i<=min(n,j+ka).
On exit, the contents of AB are destroyed.
LDAB (input) INTEGER
The leading dimension of the array AB. LDAB >= KA+1.
BB (input/output) REAL array, dimension (LDBB, N)
On entry, the upper or lower triangle of the symmetric band matrix B, stored in
the first kb+1 rows of the array. The jth column of B is stored in the jth col
umn of the array BB as follows: if UPLO = 'U', BB(kb+1+ij,j) = B(i,j) for
max(1,jkb)<=i<=j; if UPLO = 'L', BB(1+ij,j) = B(i,j) for j<=i<=min(n,j+kb).
On exit, the factor S from the split Cholesky factorization B = S**T*S, as
returned by SPBSTF.
LDBB (input) INTEGER
The leading dimension of the array BB. LDBB >= KB+1.
W (output) REAL array, dimension (N)
If INFO = 0, the eigenvalues in ascending order.
Z (output) REAL array, dimension (LDZ, N)
If JOBZ = 'V', then if INFO = 0, Z contains the matrix Z of eigenvectors, with the
ith column of Z holding the eigenvector associated with W(i). The eigenvectors
are normalized so that Z**T*B*Z = I. If JOBZ = 'N', then Z is not referenced.
LDZ (input) INTEGER
The leading dimension of the array Z. LDZ >= 1, and if JOBZ = 'V', LDZ >= N.
WORK (workspace) REAL array, dimension (3*N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
> 0: if INFO = i, and i is:
<= N: the algorithm failed to converge: i offdiagonal elements of an intermedi
ate tridiagonal form did not converge to zero; > N: if INFO = N + i, for 1 <= i
<= N, then SPBSTF
returned INFO = i: B is not positive definite. The factorization of B could not
be completed and no eigenvalues or eigenvectors were computed.
LAPACK version 3.0 15 June 2000 SSBGV(l) 
