CSTT22  checks a set of M eigenvalues and eigenvectors,


     A U = U S


 where A is Hermitian tridiagonal, the columns of U are unitary,


 and S is diagonal (if KBAND=0) or Hermitian 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, CSTT22 does nothing.


          It must be at least zero.

M

          M is INTEGER


          The number of eigenpairs to check.  If it is zero, CSTT22


          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 Hermitian tri-diagonal.

AD

          AD is REAL array, dimension (N)


          The diagonal of the original (unfactored) matrix A.  A is


          assumed to be Hermitian tridiagonal.

AE

          AE is REAL array, dimension (N)


          The off-diagonal of the original (unfactored) matrix A.  A


          is assumed to be Hermitian tridiagonal.  AE(1) is ignored,


          AE(2) is the (1,2) and (2,1) element, etc.

SD

          SD is REAL array, dimension (N)


          The diagonal of the (Hermitian tri-) diagonal matrix S.

SE

          SE is REAL array, dimension (N)


          The off-diagonal of the (Hermitian 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 REAL array, dimension (LDU, N)


          The unitary matrix in the decomposition.

LDU

          LDU is INTEGER


          The leading dimension of U.  LDU must be at least N.

WORK

          WORK is COMPLEX array, dimension (LDWORK, M+1)

LDWORK

          LDWORK is INTEGER


          The leading dimension of WORK.  LDWORK must be at least


          max(1,M).

RWORK

          RWORK is REAL array, dimension (N)

RESULT

          RESULT is REAL 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.