zstt22.f - Man Page

subroutine zstt22 (n, m, kband, ad, ae, sd, se, u, ldu, work, ldwork, rwork, result)
ZSTT22

ZSTT22

Purpose:

 ZSTT22  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 )

Parameters

N

          N is INTEGER
          The size of the matrix.  If it is zero, ZSTT22 does nothing.
          It must be at least zero.

M

          M is INTEGER
          The number of eigenpairs to check.  If it is zero, ZSTT22
          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 DOUBLE PRECISION array, dimension (N)
          The diagonal of the original (unfactored) matrix A.  A is
          assumed to be Hermitian tridiagonal.

AE

          AE is DOUBLE PRECISION 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 DOUBLE PRECISION array, dimension (N)
          The diagonal of the (Hermitian tri-) diagonal matrix S.

SE

          SE is DOUBLE PRECISION 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 DOUBLE PRECISION 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*16 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 DOUBLE PRECISION array, dimension (N)

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.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 143 of file zstt22.f.