dsbev.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 230 行 · 第 1/2 页

</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="DLASCL.98"></a><a href="dlascl.f.html#DLASCL.1">DLASCL</a>, <a name="DSBTRD.98"></a><a href="dsbtrd.f.html#DSBTRD.1">DSBTRD</a>, DSCAL, <a name="DSTEQR.98"></a><a href="dsteqr.f.html#DSTEQR.1">DSTEQR</a>, <a name="DSTERF.98"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>, <a name="XERBLA.98"></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.107"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'V'</span> )
      LOWER = <a name="LSAME.108"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'L'</span> )
<span class="comment">*</span><span class="comment">
</span>      INFO = 0
      IF( .NOT.( WANTZ .OR. <a name="LSAME.111"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'N'</span> ) ) ) THEN
         INFO = -1
      ELSE IF( .NOT.( LOWER .OR. <a name="LSAME.113"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'U'</span> ) ) ) THEN
         INFO = -2
      ELSE IF( N.LT.0 ) THEN
         INFO = -3
      ELSE IF( KD.LT.0 ) THEN
         INFO = -4
      ELSE IF( LDAB.LT.KD+1 ) THEN
         INFO = -6
      ELSE IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
         INFO = -9
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.126"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="DSBEV.126"></a><a href="dsbev.f.html#DSBEV.1">DSBEV</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
         IF( LOWER ) THEN
            W( 1 ) = AB( 1, 1 )
         ELSE
            W( 1 ) = AB( KD+1, 1 )
         END IF
         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.148"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>( <span class="string">'Safe minimum'</span> )
      EPS = <a name="DLAMCH.149"></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="DLANSB.157"></a><a href="dlansb.f.html#DLANSB.1">DLANSB</a>( <span class="string">'M'</span>, UPLO, N, KD, AB, LDAB, 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
         IF( LOWER ) THEN
            CALL <a name="DLASCL.168"></a><a href="dlascl.f.html#DLASCL.1">DLASCL</a>( <span class="string">'B'</span>, KD, KD, ONE, SIGMA, N, N, AB, LDAB, INFO )
         ELSE
            CALL <a name="DLASCL.170"></a><a href="dlascl.f.html#DLASCL.1">DLASCL</a>( <span class="string">'Q'</span>, KD, KD, ONE, SIGMA, N, N, AB, LDAB, INFO )
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Call <a name="DSBTRD.174"></a><a href="dsbtrd.f.html#DSBTRD.1">DSBTRD</a> to reduce symmetric band matrix to tridiagonal form.
</span><span class="comment">*</span><span class="comment">
</span>      INDE = 1
      INDWRK = INDE + N
      CALL <a name="DSBTRD.178"></a><a href="dsbtrd.f.html#DSBTRD.1">DSBTRD</a>( JOBZ, UPLO, N, KD, AB, LDAB, W, WORK( INDE ), Z, LDZ,
     $             WORK( INDWRK ), IINFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     For eigenvalues only, call <a name="DSTERF.181"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>.  For eigenvectors, call <a name="SSTEQR.181"></a><a href="ssteqr.f.html#SSTEQR.1">SSTEQR</a>.
</span><span class="comment">*</span><span class="comment">
</span>      IF( .NOT.WANTZ ) THEN
         CALL <a name="DSTERF.184"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>( N, W, WORK( INDE ), INFO )
      ELSE
         CALL <a name="DSTEQR.186"></a><a href="dsteqr.f.html#DSTEQR.1">DSTEQR</a>( JOBZ, N, W, WORK( INDE ), Z, LDZ, WORK( INDWRK ),
     $                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="DSBEV.203"></a><a href="dsbev.f.html#DSBEV.1">DSBEV</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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