zstedc.f.html

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</span><span class="comment">*</span><span class="comment">          of the WORK, RWORK and IWORK arrays, and no error message
</span><span class="comment">*</span><span class="comment">          related to LWORK or LRWORK or LIWORK is issued by <a name="XERBLA.126"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INFO    (output) INTEGER
</span><span class="comment">*</span><span class="comment">          = 0:  successful exit.
</span><span class="comment">*</span><span class="comment">          &lt; 0:  if INFO = -i, the i-th argument had an illegal value.
</span><span class="comment">*</span><span class="comment">          &gt; 0:  The algorithm failed to compute an eigenvalue while
</span><span class="comment">*</span><span class="comment">                working on the submatrix lying in rows and columns
</span><span class="comment">*</span><span class="comment">                INFO/(N+1) through mod(INFO,N+1).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Further Details
</span><span class="comment">*</span><span class="comment">  ===============
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Based on contributions by
</span><span class="comment">*</span><span class="comment">     Jeff Rutter, Computer Science Division, University of California
</span><span class="comment">*</span><span class="comment">     at Berkeley, USA
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      DOUBLE PRECISION   ZERO, ONE, TWO
      PARAMETER          ( ZERO = 0.0D0, ONE = 1.0D0, TWO = 2.0D0 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      LOGICAL            LQUERY
      INTEGER            FINISH, I, ICOMPZ, II, J, K, LGN, LIWMIN, LL,
     $                   LRWMIN, LWMIN, M, SMLSIZ, START
      DOUBLE PRECISION   EPS, ORGNRM, P, TINY
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Functions ..
</span>      LOGICAL            <a name="LSAME.155"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      INTEGER            <a name="ILAENV.156"></a><a href="hfy-index.html#ILAENV">ILAENV</a>
      DOUBLE PRECISION   <a name="DLAMCH.157"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>, <a name="DLANST.157"></a><a href="dlanst.f.html#DLANST.1">DLANST</a>
      EXTERNAL           <a name="LSAME.158"></a><a href="lsame.f.html#LSAME.1">LSAME</a>, <a name="ILAENV.158"></a><a href="hfy-index.html#ILAENV">ILAENV</a>, <a name="DLAMCH.158"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>, <a name="DLANST.158"></a><a href="dlanst.f.html#DLANST.1">DLANST</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="DLASCL.161"></a><a href="dlascl.f.html#DLASCL.1">DLASCL</a>, <a name="DLASET.161"></a><a href="dlaset.f.html#DLASET.1">DLASET</a>, <a name="DSTEDC.161"></a><a href="dstedc.f.html#DSTEDC.1">DSTEDC</a>, <a name="DSTEQR.161"></a><a href="dsteqr.f.html#DSTEQR.1">DSTEQR</a>, <a name="DSTERF.161"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>, <a name="XERBLA.161"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>,
     $                   <a name="ZLACPY.162"></a><a href="zlacpy.f.html#ZLACPY.1">ZLACPY</a>, <a name="ZLACRM.162"></a><a href="zlacrm.f.html#ZLACRM.1">ZLACRM</a>, <a name="ZLAED0.162"></a><a href="zlaed0.f.html#ZLAED0.1">ZLAED0</a>, <a name="ZSTEQR.162"></a><a href="zsteqr.f.html#ZSTEQR.1">ZSTEQR</a>, ZSWAP
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          ABS, DBLE, INT, LOG, MAX, MOD, SQRT
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Test the input parameters.
</span><span class="comment">*</span><span class="comment">
</span>      INFO = 0
      LQUERY = ( LWORK.EQ.-1 .OR. LRWORK.EQ.-1 .OR. LIWORK.EQ.-1 )
<span class="comment">*</span><span class="comment">
</span>      IF( <a name="LSAME.174"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( COMPZ, <span class="string">'N'</span> ) ) THEN
         ICOMPZ = 0
      ELSE IF( <a name="LSAME.176"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( COMPZ, <span class="string">'V'</span> ) ) THEN
         ICOMPZ = 1
      ELSE IF( <a name="LSAME.178"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( COMPZ, <span class="string">'I'</span> ) ) THEN
         ICOMPZ = 2
      ELSE
         ICOMPZ = -1
      END IF
      IF( ICOMPZ.LT.0 ) THEN
         INFO = -1
      ELSE IF( N.LT.0 ) THEN
         INFO = -2
      ELSE IF( ( LDZ.LT.1 ) .OR.
     $         ( ICOMPZ.GT.0 .AND. LDZ.LT.MAX( 1, N ) ) ) THEN
         INFO = -6
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.EQ.0 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Compute the workspace requirements
</span><span class="comment">*</span><span class="comment">
</span>         SMLSIZ = <a name="ILAENV.196"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 9, <span class="string">'<a name="ZSTEDC.196"></a><a href="zstedc.f.html#ZSTEDC.1">ZSTEDC</a>'</span>, <span class="string">' '</span>, 0, 0, 0, 0 )
         IF( N.LE.1 .OR. ICOMPZ.EQ.0 ) THEN
            LWMIN = 1
            LIWMIN = 1
            LRWMIN = 1
         ELSE IF( N.LE.SMLSIZ ) THEN
            LWMIN = 1
            LIWMIN = 1
            LRWMIN = 2*( N - 1 )
         ELSE IF( ICOMPZ.EQ.1 ) THEN
            LGN = INT( LOG( DBLE( N ) ) / LOG( TWO ) )
            IF( 2**LGN.LT.N )
     $         LGN = LGN + 1
            IF( 2**LGN.LT.N )
     $         LGN = LGN + 1
            LWMIN = N*N
            LRWMIN = 1 + 3*N + 2*N*LGN + 3*N**2
            LIWMIN = 6 + 6*N + 5*N*LGN
         ELSE IF( ICOMPZ.EQ.2 ) THEN
            LWMIN = 1
            LRWMIN = 1 + 4*N + 2*N**2
            LIWMIN = 3 + 5*N
         END IF
         WORK( 1 ) = LWMIN
         RWORK( 1 ) = LRWMIN
         IWORK( 1 ) = LIWMIN
<span class="comment">*</span><span class="comment">
</span>         IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -8
         ELSE IF( LRWORK.LT.LRWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -10
         ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -12
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.233"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="ZSTEDC.233"></a><a href="zstedc.f.html#ZSTEDC.1">ZSTEDC</a>'</span>, -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Quick return if possible
</span><span class="comment">*</span><span class="comment">
</span>      IF( N.EQ.0 )
     $   RETURN
      IF( N.EQ.1 ) THEN
         IF( ICOMPZ.NE.0 )
     $      Z( 1, 1 ) = ONE
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     If the following conditional clause is removed, then the routine
</span><span class="comment">*</span><span class="comment">     will use the Divide and Conquer routine to compute only the
</span><span class="comment">*</span><span class="comment">     eigenvalues, which requires (3N + 3N**2) real workspace and
</span><span class="comment">*</span><span class="comment">     (2 + 5N + 2N lg(N)) integer workspace.
</span><span class="comment">*</span><span class="comment">     Since on many architectures <a name="DSTERF.253"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a> is much faster than any other
</span><span class="comment">*</span><span class="comment">     algorithm for finding eigenvalues only, it is used here
</span><span class="comment">*</span><span class="comment">     as the default. If the conditional clause is removed, then
</span><span class="comment">*</span><span class="comment">     information on the size of workspace needs to be changed.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     If COMPZ = 'N', use <a name="DSTERF.258"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a> to compute the eigenvalues.
</span><span class="comment">*</span><span class="comment">
</span>      IF( ICOMPZ.EQ.0 ) THEN
         CALL <a name="DSTERF.261"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>( N, D, E, INFO )
         GO TO 70
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     If N is smaller than the minimum divide size (SMLSIZ+1), then
</span><span class="comment">*</span><span class="comment">     solve the problem with another solver.
</span><span class="comment">*</span><span class="comment">