dstevr.f

famous linear algebra library (LAPACK) ports to windows

*
*     Test the input parameters.
*
      IEEEOK = ILAENV( 10, 'DSTEVR', 'N', 1, 2, 3, 4 )
*
      WANTZ = LSAME( JOBZ, 'V' )
      ALLEIG = LSAME( RANGE, 'A' )
      VALEIG = LSAME( RANGE, 'V' )
      INDEIG = LSAME( RANGE, 'I' )
*
      LQUERY = ( ( LWORK.EQ.-1 ) .OR. ( LIWORK.EQ.-1 ) )
      LWMIN = MAX( 1, 20*N )
      LIWMIN = MAX( 1, 10*N )
*
*
      INFO = 0
      IF( .NOT.( WANTZ .OR. LSAME( JOBZ, 'N' ) ) ) THEN
         INFO = -1
      ELSE IF( .NOT.( ALLEIG .OR. VALEIG .OR. INDEIG ) ) THEN
         INFO = -2
      ELSE IF( N.LT.0 ) THEN
         INFO = -3
      ELSE
         IF( VALEIG ) THEN
            IF( N.GT.0 .AND. VU.LE.VL )
     $         INFO = -7
         ELSE IF( INDEIG ) THEN
            IF( IL.LT.1 .OR. IL.GT.MAX( 1, N ) ) THEN
               INFO = -8
            ELSE IF( IU.LT.MIN( N, IL ) .OR. IU.GT.N ) THEN
               INFO = -9
            END IF
         END IF
      END IF
      IF( INFO.EQ.0 ) THEN
         IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
            INFO = -14
         END IF
      END IF
*
      IF( INFO.EQ.0 ) THEN
         WORK( 1 ) = LWMIN
         IWORK( 1 ) = LIWMIN
*
         IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -17
         ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -19
         END IF
      END IF
*
      IF( INFO.NE.0 ) THEN
         CALL XERBLA( 'DSTEVR', -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
*
*     Quick return if possible
*
      M = 0
      IF( N.EQ.0 )
     $   RETURN
*
      IF( N.EQ.1 ) THEN
         IF( ALLEIG .OR. INDEIG ) THEN
            M = 1
            W( 1 ) = D( 1 )
         ELSE
            IF( VL.LT.D( 1 ) .AND. VU.GE.D( 1 ) ) THEN
               M = 1
               W( 1 ) = D( 1 )
            END IF
         END IF
         IF( WANTZ )
     $      Z( 1, 1 ) = ONE
         RETURN
      END IF
*
*     Get machine constants.
*
      SAFMIN = DLAMCH( 'Safe minimum' )
      EPS = DLAMCH( 'Precision' )
      SMLNUM = SAFMIN / EPS
      BIGNUM = ONE / SMLNUM
      RMIN = SQRT( SMLNUM )
      RMAX = MIN( SQRT( BIGNUM ), ONE / SQRT( SQRT( SAFMIN ) ) )
*
*
*     Scale matrix to allowable range, if necessary.
*
      ISCALE = 0
      VLL = VL
      VUU = VU
*
      TNRM = DLANST( 'M', N, D, E )
      IF( TNRM.GT.ZERO .AND. TNRM.LT.RMIN ) THEN
         ISCALE = 1
         SIGMA = RMIN / TNRM
      ELSE IF( TNRM.GT.RMAX ) THEN
         ISCALE = 1
         SIGMA = RMAX / TNRM
      END IF
      IF( ISCALE.EQ.1 ) THEN
         CALL DSCAL( N, SIGMA, D, 1 )
         CALL DSCAL( N-1, SIGMA, E( 1 ), 1 )
         IF( VALEIG ) THEN
            VLL = VL*SIGMA
            VUU = VU*SIGMA
         END IF
      END IF

*     Initialize indices into workspaces.  Note: These indices are used only
*     if DSTERF or DSTEMR fail.

*     IWORK(INDIBL:INDIBL+M-1) corresponds to IBLOCK in DSTEBZ and
*     stores the block indices of each of the M<=N eigenvalues.
      INDIBL = 1
*     IWORK(INDISP:INDISP+NSPLIT-1) corresponds to ISPLIT in DSTEBZ and
*     stores the starting and finishing indices of each block.
      INDISP = INDIBL + N
*     IWORK(INDIFL:INDIFL+N-1) stores the indices of eigenvectors
*     that corresponding to eigenvectors that fail to converge in
*     DSTEIN.  This information is discarded; if any fail, the driver
*     returns INFO > 0.
      INDIFL = INDISP + N
*     INDIWO is the offset of the remaining integer workspace.
      INDIWO = INDISP + N
*
*     If all eigenvalues are desired, then
*     call DSTERF or DSTEMR.  If this fails for some eigenvalue, then
*     try DSTEBZ.
*
*
      TEST = .FALSE.
      IF( INDEIG ) THEN
         IF( IL.EQ.1 .AND. IU.EQ.N ) THEN
            TEST = .TRUE.
         END IF
      END IF
      IF( ( ALLEIG .OR. TEST ) .AND. IEEEOK.EQ.1 ) THEN
         CALL DCOPY( N-1, E( 1 ), 1, WORK( 1 ), 1 )
         IF( .NOT.WANTZ ) THEN
            CALL DCOPY( N, D, 1, W, 1 )
            CALL DSTERF( N, W, WORK, INFO )
         ELSE
            CALL DCOPY( N, D, 1, WORK( N+1 ), 1 )
            IF (ABSTOL .LE. TWO*N*EPS) THEN
               TRYRAC = .TRUE.
            ELSE
               TRYRAC = .FALSE.
            END IF
            CALL DSTEMR( JOBZ, 'A', N, WORK( N+1 ), WORK, VL, VU, IL,
     $                   IU, M, W, Z, LDZ, N, ISUPPZ, TRYRAC,
     $                   WORK( 2*N+1 ), LWORK-2*N, IWORK, LIWORK, INFO )
*
         END IF
         IF( INFO.EQ.0 ) THEN
            M = N
            GO TO 10
         END IF
         INFO = 0
      END IF
*
*     Otherwise, call DSTEBZ and, if eigenvectors are desired, DSTEIN.
*
      IF( WANTZ ) THEN
         ORDER = 'B'
      ELSE
         ORDER = 'E'
      END IF

      CALL DSTEBZ( RANGE, ORDER, N, VLL, VUU, IL, IU, ABSTOL, D, E, M,
     $             NSPLIT, W, IWORK( INDIBL ), IWORK( INDISP ), WORK,
     $             IWORK( INDIWO ), INFO )
*
      IF( WANTZ ) THEN
         CALL DSTEIN( N, D, E, M, W, IWORK( INDIBL ), IWORK( INDISP ),
     $                Z, LDZ, WORK, IWORK( INDIWO ), IWORK( INDIFL ),
     $                INFO )
      END IF
*
*     If matrix was scaled, then rescale eigenvalues appropriately.
*
   10 CONTINUE
      IF( ISCALE.EQ.1 ) THEN
         IF( INFO.EQ.0 ) THEN
            IMAX = M
         ELSE
            IMAX = INFO - 1
         END IF
         CALL DSCAL( IMAX, ONE / SIGMA, W, 1 )
      END IF
*
*     If eigenvalues are not in order, then sort them, along with
*     eigenvectors.
*
      IF( WANTZ ) THEN
         DO 30 J = 1, M - 1
            I = 0
            TMP1 = W( J )
            DO 20 JJ = J + 1, M
               IF( W( JJ ).LT.TMP1 ) THEN
                  I = JJ
                  TMP1 = W( JJ )
               END IF
   20       CONTINUE
*
            IF( I.NE.0 ) THEN
               ITMP1 = IWORK( I )
               W( I ) = W( J )
               IWORK( I ) = IWORK( J )
               W( J ) = TMP1
               IWORK( J ) = ITMP1
               CALL DSWAP( N, Z( 1, I ), 1, Z( 1, J ), 1 )
            END IF
   30    CONTINUE
      END IF
*
*      Causes problems with tests 19 & 20:
*      IF (wantz .and. INDEIG ) Z( 1,1) = Z(1,1) / 1.002 + .002
*
*
      WORK( 1 ) = LWMIN
      IWORK( 1 ) = LIWMIN
      RETURN
*
*     End of DSTEVR
*
      END