dspev.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 212 行 · 第 1/2 页

</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="DOPGTR.89"></a><a href="dopgtr.f.html#DOPGTR.1">DOPGTR</a>, DSCAL, <a name="DSPTRD.89"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a>, <a name="DSTEQR.89"></a><a href="dsteqr.f.html#DSTEQR.1">DSTEQR</a>, <a name="DSTERF.89"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>, <a name="XERBLA.89"></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.98"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'V'</span> )
<span class="comment">*</span><span class="comment">
</span>      INFO = 0
      IF( .NOT.( WANTZ .OR. <a name="LSAME.101"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'N'</span> ) ) ) THEN
         INFO = -1
      ELSE IF( .NOT.( <a name="LSAME.103"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'U'</span> ) .OR. <a name="LSAME.103"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'L'</span> ) ) )
     $          THEN
         INFO = -2
      ELSE IF( N.LT.0 ) THEN
         INFO = -3
      ELSE IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
         INFO = -7
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.113"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="DSPEV.113"></a><a href="dspev.f.html#DSPEV.1">DSPEV</a> '</span>, -INFO )
         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
         W( 1 ) = AP( 1 )
         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.131"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>( <span class="string">'Safe minimum'</span> )
      EPS = <a name="DLAMCH.132"></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>      ANRM = <a name="DLANSP.140"></a><a href="dlansp.f.html#DLANSP.1">DLANSP</a>( <span class="string">'M'</span>, UPLO, N, AP, WORK )
      ISCALE = 0
      IF( ANRM.GT.ZERO .AND. ANRM.LT.RMIN ) THEN
         ISCALE = 1
         SIGMA = RMIN / ANRM
      ELSE IF( ANRM.GT.RMAX ) THEN
         ISCALE = 1
         SIGMA = RMAX / ANRM
      END IF
      IF( ISCALE.EQ.1 ) THEN
         CALL DSCAL( ( N*( N+1 ) ) / 2, SIGMA, AP, 1 )
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Call <a name="DSPTRD.153"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a> to reduce symmetric packed matrix to tridiagonal form.
</span><span class="comment">*</span><span class="comment">
</span>      INDE = 1
      INDTAU = INDE + N
      CALL <a name="DSPTRD.157"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a>( UPLO, N, AP, W, WORK( INDE ), WORK( INDTAU ), IINFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     For eigenvalues only, call <a name="DSTERF.159"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>.  For eigenvectors, first call
</span><span class="comment">*</span><span class="comment">     <a name="DOPGTR.160"></a><a href="dopgtr.f.html#DOPGTR.1">DOPGTR</a> to generate the orthogonal matrix, then call <a name="DSTEQR.160"></a><a href="dsteqr.f.html#DSTEQR.1">DSTEQR</a>.
</span><span class="comment">*</span><span class="comment">
</span>      IF( .NOT.WANTZ ) THEN
         CALL <a name="DSTERF.163"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>( N, W, WORK( INDE ), INFO )
      ELSE
         INDWRK = INDTAU + N
         CALL <a name="DOPGTR.166"></a><a href="dopgtr.f.html#DOPGTR.1">DOPGTR</a>( UPLO, N, AP, WORK( INDTAU ), Z, LDZ,
     $                WORK( INDWRK ), IINFO )
         CALL <a name="DSTEQR.168"></a><a href="dsteqr.f.html#DSTEQR.1">DSTEQR</a>( JOBZ, N, W, WORK( INDE ), Z, LDZ, WORK( INDTAU ),
     $                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 ) THEN
         IF( INFO.EQ.0 ) THEN
            IMAX = N
         ELSE
            IMAX = INFO - 1
         END IF
         CALL DSCAL( IMAX, ONE / SIGMA, W, 1 )
      END IF
<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="DSPEV.185"></a><a href="dspev.f.html#DSPEV.1">DSPEV</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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