dstt22.f3

!>
!> DSTT22  checks a set of M eigenvalues and eigenvectors,
!>
!>     A U = U S
!>
!> where A is symmetric tridiagonal, the columns of U are orthogonal,
!> and S is diagonal (if KBAND=0) or symmetric tridiagonal (if KBAND=1).
!> Two tests are performed:
!>
!>    RESULT(1) = | U' A U - S | / ( |A| m ulp )
!>
!>    RESULT(2) = | I - U'U | / ( m ulp )
!> 

N

!>          N is INTEGER
!>          The size of the matrix.  If it is zero, DSTT22 does nothing.
!>          It must be at least zero.
!> 

M

!>          M is INTEGER
!>          The number of eigenpairs to check.  If it is zero, DSTT22
!>          does nothing.  It must be at least zero.
!> 

KBAND

!>          KBAND is INTEGER
!>          The bandwidth of the matrix S.  It may only be zero or one.
!>          If zero, then S is diagonal, and SE is not referenced.  If
!>          one, then S is symmetric tri-diagonal.
!> 

AD

!>          AD is DOUBLE PRECISION array, dimension (N)
!>          The diagonal of the original (unfactored) matrix A.  A is
!>          assumed to be symmetric tridiagonal.
!> 

AE

!>          AE is DOUBLE PRECISION array, dimension (N)
!>          The off-diagonal of the original (unfactored) matrix A.  A
!>          is assumed to be symmetric tridiagonal.  AE(1) is ignored,
!>          AE(2) is the (1,2) and (2,1) element, etc.
!> 

SD

!>          SD is DOUBLE PRECISION array, dimension (N)
!>          The diagonal of the (symmetric tri-) diagonal matrix S.
!> 

SE

!>          SE is DOUBLE PRECISION array, dimension (N)
!>          The off-diagonal of the (symmetric tri-) diagonal matrix S.
!>          Not referenced if KBSND=0.  If KBAND=1, then AE(1) is
!>          ignored, SE(2) is the (1,2) and (2,1) element, etc.
!> 

U

!>          U is DOUBLE PRECISION array, dimension (LDU, N)
!>          The orthogonal matrix in the decomposition.
!> 

LDU

!>          LDU is INTEGER
!>          The leading dimension of U.  LDU must be at least N.
!> 

WORK

!>          WORK is DOUBLE PRECISION array, dimension (LDWORK, M+1)
!> 

LDWORK

!>          LDWORK is INTEGER
!>          The leading dimension of WORK.  LDWORK must be at least
!>          max(1,M).
!> 

RESULT

!>          RESULT is DOUBLE PRECISION array, dimension (2)
!>          The values computed by the two tests described above.  The
!>          values are currently limited to 1/ulp, to avoid overflow.
!> 

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.