zstt22.f

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*> \brief \b ZSTT22
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at 
*            http://www.netlib.org/lapack/explore-html/ 
*
*  Definition:
*  ===========
*
*       SUBROUTINE ZSTT22( N, M, KBAND, AD, AE, SD, SE, U, LDU, WORK,
*                          LDWORK, RWORK, RESULT )
* 
*       .. Scalar Arguments ..
*       INTEGER            KBAND, LDU, LDWORK, M, N
*       ..
*       .. Array Arguments ..
*       DOUBLE PRECISION   AD( * ), AE( * ), RESULT( 2 ), RWORK( * ),
*      $                   SD( * ), SE( * )
*       COMPLEX*16         U( LDU, * ), WORK( LDWORK, * )
*       ..
*  
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> 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 )
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The size of the matrix.  If it is zero, ZSTT22 does nothing.
*>          It must be at least zero.
*> \endverbatim
*>
*> \param[in] M
*> \verbatim
*>          M is INTEGER
*>          The number of eigenpairs to check.  If it is zero, ZSTT22
*>          does nothing.  It must be at least zero.
*> \endverbatim
*>
*> \param[in] KBAND
*> \verbatim
*>          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.
*> \endverbatim
*>
*> \param[in] AD
*> \verbatim
*>          AD is DOUBLE PRECISION array, dimension (N)
*>          The diagonal of the original (unfactored) matrix A.  A is
*>          assumed to be Hermitian tridiagonal.
*> \endverbatim
*>
*> \param[in] AE
*> \verbatim
*>          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.
*> \endverbatim
*>
*> \param[in] SD
*> \verbatim
*>          SD is DOUBLE PRECISION array, dimension (N)
*>          The diagonal of the (Hermitian tri-) diagonal matrix S.
*> \endverbatim
*>
*> \param[in] SE
*> \verbatim
*>          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.
*> \endverbatim
*>
*> \param[in] U
*> \verbatim
*>          U is DOUBLE PRECISION array, dimension (LDU, N)
*>          The unitary matrix in the decomposition.
*> \endverbatim
*>
*> \param[in] LDU
*> \verbatim
*>          LDU is INTEGER
*>          The leading dimension of U.  LDU must be at least N.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*>          WORK is COMPLEX*16 array, dimension (LDWORK, M+1)
*> \endverbatim
*>
*> \param[in] LDWORK
*> \verbatim
*>          LDWORK is INTEGER
*>          The leading dimension of WORK.  LDWORK must be at least
*>          max(1,M).
*> \endverbatim
*>
*> \param[out] RWORK
*> \verbatim
*>          RWORK is DOUBLE PRECISION array, dimension (N)
*> \endverbatim
*>
*> \param[out] RESULT
*> \verbatim
*>          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.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee 
*> \author Univ. of California Berkeley 
*> \author Univ. of Colorado Denver 
*> \author NAG Ltd. 
*
*> \date November 2011
*
*> \ingroup complex16_eig
*
*  =====================================================================
      SUBROUTINE zstt22( N, M, KBAND, AD, AE, SD, SE, U, LDU, WORK,
     $                   ldwork, rwork, result )
*
*  -- LAPACK test routine (version 3.4.0) --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2011
*
*     .. Scalar Arguments ..
      INTEGER            kband, ldu, ldwork, m, n
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   ad( * ), ae( * ), result( 2 ), rwork( * ),
     $                   sd( * ), se( * )
      COMPLEX*16         u( ldu, * ), work( ldwork, * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   zero, one
      parameter( zero = 0.0d0, one = 1.0d0 )
      COMPLEX*16         czero, cone
      parameter( czero = ( 0.0d+0, 0.0d+0 ),
     $                   cone = ( 1.0d+0, 0.0d+0 ) )
*     ..
*     .. Local Scalars ..
      INTEGER            i, j, k
      DOUBLE PRECISION   anorm, ulp, unfl, wnorm
      COMPLEX*16         aukj
*     ..
*     .. External Functions ..
      DOUBLE PRECISION   dlamch, zlange, zlansy
      EXTERNAL           dlamch, zlange, zlansy
*     ..
*     .. External Subroutines ..
      EXTERNAL           zgemm
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          abs, dble, max, min
*     ..
*     .. Executable Statements ..
*
      result( 1 ) = zero
      result( 2 ) = zero
      IF( n.LE.0 .OR. m.LE.0 )
     $   return
*
      unfl = dlamch( 'Safe minimum' )
      ulp = dlamch( 'Epsilon' )
*
*     Do Test 1
*
*     Compute the 1-norm of A.
*
      IF( n.GT.1 ) THEN
         anorm = abs( ad( 1 ) ) + abs( ae( 1 ) )
         DO 10 j = 2, n - 1
            anorm = max( anorm, abs( ad( j ) )+abs( ae( j ) )+
     $              abs( ae( j-1 ) ) )
   10    continue
         anorm = max( anorm, abs( ad( n ) )+abs( ae( n-1 ) ) )
      ELSE
         anorm = abs( ad( 1 ) )
      END IF
      anorm = max( anorm, unfl )
*
*     Norm of U*AU - S
*
      DO 40 i = 1, m
         DO 30 j = 1, m
            work( i, j ) = czero
            DO 20 k = 1, n
               aukj = ad( k )*u( k, j )
               IF( k.NE.n )
     $            aukj = aukj + ae( k )*u( k+1, j )
               IF( k.NE.1 )
     $            aukj = aukj + ae( k-1 )*u( k-1, j )
               work( i, j ) = work( i, j ) + u( k, i )*aukj
   20       continue
   30    continue
         work( i, i ) = work( i, i ) - sd( i )
         IF( kband.EQ.1 ) THEN
            IF( i.NE.1 )
     $         work( i, i-1 ) = work( i, i-1 ) - se( i-1 )
            IF( i.NE.n )
     $         work( i, i+1 ) = work( i, i+1 ) - se( i )
         END IF
   40 continue
*
      wnorm = zlansy( '1', 'L', m, work, m, rwork )
*
      IF( anorm.GT.wnorm ) THEN
         result( 1 ) = ( wnorm / anorm ) / ( m*ulp )
      ELSE
         IF( anorm.LT.one ) THEN
            result( 1 ) = ( min( wnorm, m*anorm ) / anorm ) / ( m*ulp )
         ELSE
            result( 1 ) = min( wnorm / anorm, dble( m ) ) / ( m*ulp )
         END IF
      END IF
*
*     Do Test 2
*
*     Compute  U*U - I
*
      CALL zgemm( 'T', 'N', m, m, n, cone, u, ldu, u, ldu, czero, work,
     $            m )
*
      DO 50 j = 1, m
         work( j, j ) = work( j, j ) - one
   50 continue
*
      result( 2 ) = min( dble( m ), zlange( '1', m, m, work, m,
     $              rwork ) ) / ( m*ulp )
*
      return
*
*     End of ZSTT22
*
      END