dstevd.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 244 行 · 第 1/2 页

</span>      LOGICAL            LQUERY, WANTZ
      INTEGER            ISCALE, LIWMIN, LWMIN
      DOUBLE PRECISION   BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA, SMLNUM,
     $                   TNRM
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Functions ..
</span>      LOGICAL            <a name="LSAME.110"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      DOUBLE PRECISION   <a name="DLAMCH.111"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>, <a name="DLANST.111"></a><a href="dlanst.f.html#DLANST.1">DLANST</a>
      EXTERNAL           <a name="LSAME.112"></a><a href="lsame.f.html#LSAME.1">LSAME</a>, <a name="DLAMCH.112"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>, <a name="DLANST.112"></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           DSCAL, <a name="DSTEDC.115"></a><a href="dstedc.f.html#DSTEDC.1">DSTEDC</a>, <a name="DSTERF.115"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>, <a name="XERBLA.115"></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          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>      WANTZ = <a name="LSAME.124"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'V'</span> )
      LQUERY = ( LWORK.EQ.-1 .OR. LIWORK.EQ.-1 )
<span class="comment">*</span><span class="comment">
</span>      INFO = 0
      LIWMIN = 1
      LWMIN = 1
      IF( N.GT.1 .AND. WANTZ ) THEN
         LWMIN = 1 + 4*N + N**2
         LIWMIN = 3 + 5*N
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( .NOT.( WANTZ .OR. <a name="LSAME.135"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'N'</span> ) ) ) THEN
         INFO = -1
      ELSE IF( N.LT.0 ) THEN
         INFO = -2
      ELSE IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
         INFO = -6
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.EQ.0 ) THEN
         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.155"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="DSTEVD.155"></a><a href="dstevd.f.html#DSTEVD.1">DSTEVD</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
<span class="comment">*</span><span class="comment">
</span>      IF( N.EQ.1 ) THEN
         IF( WANTZ )
     $      Z( 1, 1 ) = ONE
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Get machine constants.
</span><span class="comment">*</span><span class="comment">
</span>      SAFMIN = <a name="DLAMCH.174"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>( <span class="string">'Safe minimum'</span> )
      EPS = <a name="DLAMCH.175"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>( <span class="string">'Precision'</span> )
      SMLNUM = SAFMIN / EPS
      BIGNUM = ONE / SMLNUM
      RMIN = SQRT( SMLNUM )
      RMAX = SQRT( BIGNUM )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Scale matrix to allowable range, if necessary.
</span><span class="comment">*</span><span class="comment">
</span>      ISCALE = 0
      TNRM = <a name="DLANST.184"></a><a href="dlanst.f.html#DLANST.1">DLANST</a>( <span class="string">'M'</span>, 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 )
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     For eigenvalues only, call <a name="DSTERF.197"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>.  For eigenvalues and
</span><span class="comment">*</span><span class="comment">     eigenvectors, call <a name="DSTEDC.198"></a><a href="dstedc.f.html#DSTEDC.1">DSTEDC</a>.
</span><span class="comment">*</span><span class="comment">
</span>      IF( .NOT.WANTZ ) THEN
         CALL <a name="DSTERF.201"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>( N, D, E, INFO )
      ELSE
         CALL <a name="DSTEDC.203"></a><a href="dstedc.f.html#DSTEDC.1">DSTEDC</a>( <span class="string">'I'</span>, N, D, E, Z, LDZ, WORK, LWORK, IWORK, LIWORK,
     $                INFO )
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     If matrix was scaled, then rescale eigenvalues appropriately.
</span><span class="comment">*</span><span class="comment">
</span>      IF( ISCALE.EQ.1 )
     $   CALL DSCAL( N, ONE / SIGMA, D, 1 )
<span class="comment">*</span><span class="comment">
</span>      WORK( 1 ) = LWMIN
      IWORK( 1 ) = LIWMIN
<span class="comment">*</span><span class="comment">
</span>      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DSTEVD.217"></a><a href="dstevd.f.html#DSTEVD.1">DSTEVD</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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