sstedc.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 431 行 · 第 1/3 页

</span>      REAL               ZERO, ONE, TWO
      PARAMETER          ( ZERO = 0.0E0, ONE = 1.0E0, TWO = 2.0E0 )
<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,
     $                   LWMIN, M, SMLSIZ, START, STOREZ, STRTRW
      REAL               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.136"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      INTEGER            <a name="ILAENV.137"></a><a href="hfy-index.html#ILAENV">ILAENV</a>
      REAL               <a name="SLAMCH.138"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>, <a name="SLANST.138"></a><a href="slanst.f.html#SLANST.1">SLANST</a>
      EXTERNAL           <a name="ILAENV.139"></a><a href="hfy-index.html#ILAENV">ILAENV</a>, <a name="LSAME.139"></a><a href="lsame.f.html#LSAME.1">LSAME</a>, <a name="SLAMCH.139"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>, <a name="SLANST.139"></a><a href="slanst.f.html#SLANST.1">SLANST</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           SGEMM, <a name="SLACPY.142"></a><a href="slacpy.f.html#SLACPY.1">SLACPY</a>, <a name="SLAED0.142"></a><a href="slaed0.f.html#SLAED0.1">SLAED0</a>, <a name="SLASCL.142"></a><a href="slascl.f.html#SLASCL.1">SLASCL</a>, <a name="SLASET.142"></a><a href="slaset.f.html#SLASET.1">SLASET</a>, <a name="SLASRT.142"></a><a href="slasrt.f.html#SLASRT.1">SLASRT</a>,
     $                   <a name="SSTEQR.143"></a><a href="ssteqr.f.html#SSTEQR.1">SSTEQR</a>, <a name="SSTERF.143"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a>, SSWAP, <a name="XERBLA.143"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          ABS, INT, LOG, MAX, MOD, REAL, 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. LIWORK.EQ.-1 )
<span class="comment">*</span><span class="comment">
</span>      IF( <a name="LSAME.155"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( COMPZ, <span class="string">'N'</span> ) ) THEN
         ICOMPZ = 0
      ELSE IF( <a name="LSAME.157"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( COMPZ, <span class="string">'V'</span> ) ) THEN
         ICOMPZ = 1
      ELSE IF( <a name="LSAME.159"></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.177"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 9, <span class="string">'<a name="SSTEDC.177"></a><a href="sstedc.f.html#SSTEDC.1">SSTEDC</a>'</span>, <span class="string">' '</span>, 0, 0, 0, 0 )
         IF( N.LE.1 .OR. ICOMPZ.EQ.0 ) THEN
            LIWMIN = 1
            LWMIN = 1
         ELSE IF( N.LE.SMLSIZ ) THEN
            LIWMIN = 1
            LWMIN = 2*( N - 1 )
         ELSE
            LGN = INT( LOG( REAL( N ) )/LOG( TWO ) )
            IF( 2**LGN.LT.N )
     $         LGN = LGN + 1
            IF( 2**LGN.LT.N )
     $         LGN = LGN + 1
            IF( ICOMPZ.EQ.1 ) THEN
               LWMIN = 1 + 3*N + 2*N*LGN + 3*N**2
               LIWMIN = 6 + 6*N + 5*N*LGN
            ELSE IF( ICOMPZ.EQ.2 ) THEN
               LWMIN = 1 + 4*N + N**2
               LIWMIN = 3 + 5*N
            END IF
         END IF
         WORK( 1 ) = LWMIN
         IWORK( 1 ) = LIWMIN
<span class="comment">*</span><span class="comment">
</span>         IF( LWORK.LT.LWMIN .AND. .NOT. LQUERY ) THEN
            INFO = -8
         ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT. LQUERY ) THEN
            INFO = -10
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.209"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="SSTEDC.209"></a><a href="sstedc.f.html#SSTEDC.1">SSTEDC</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="SSTERF.229"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</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="SSTERF.234"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a> to compute the eigenvalues.
</span><span class="comment">*</span><span class="comment">
</span>      IF( ICOMPZ.EQ.0 ) THEN
         CALL <a name="SSTERF.237"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a>( N, D, E, INFO )
         GO TO 50
      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">
</span>      IF( N.LE.SMLSIZ ) THEN
<span class="comment">*</span><span class="comment">
</span>         CALL <a name="SSTEQR.246"></a><a href="ssteqr.f.html#SSTEQR.1">SSTEQR</a>( COMPZ, N, D, E, Z, LDZ, WORK, INFO )
<span class="comment">*</span><span class="comment">
</span>      ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        If COMPZ = 'V', the Z matrix must be stored elsewhere for later
</span><span class="comment">*</span><span class="comment">        use.
</span><span class="comment">*</span><span class="comment">
</span>         IF( ICOMPZ.EQ.1 ) THEN
            STOREZ = 1 + N*N
         ELSE
            STOREZ = 1
         END IF
<span class="comment">*</span><span class="comment">
</span>         IF( ICOMPZ.EQ.2 ) THEN
            CALL <a name="SLASET.260"></a><a href="slaset.f.html#SLASET.1">SLASET</a>( <span class="string">'Full'</span>, N, N, ZERO, ONE, Z, LDZ )
         END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Scale.
</span><span class="comment">*</span><span class="comment">
</span>         ORGNRM = <a name="SLANST.265"></a><a href="slanst.f.html#SLANST.1">SLANST</a>( <span class="string">'M'</span>, N, D, E )
         IF( ORGNRM.EQ.ZERO )
     $      GO TO 50
<span class="comment">*</span><span class="comment">
</span>         EPS = <a name="SLAMCH.269"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>( <span class="string">'Epsilon'</span> )