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来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 233 行 · 第 1/2 页

<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           DSCAL, <a name="DSTERF.101"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>, <a name="XERBLA.101"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>, <a name="ZHBTRD.101"></a><a href="zhbtrd.f.html#ZHBTRD.1">ZHBTRD</a>, <a name="ZLASCL.101"></a><a href="zlascl.f.html#ZLASCL.1">ZLASCL</a>, <a name="ZSTEQR.101"></a><a href="zsteqr.f.html#ZSTEQR.1">ZSTEQR</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.110"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'V'</span> )
      LOWER = <a name="LSAME.111"></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.114"></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.116"></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.129"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="ZHBEV.129"></a><a href="zhbev.f.html#ZHBEV.1">ZHBEV</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.151"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>( <span class="string">'Safe minimum'</span> )
      EPS = <a name="DLAMCH.152"></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="ZLANHB.160"></a><a href="zlanhb.f.html#ZLANHB.1">ZLANHB</a>( <span class="string">'M'</span>, UPLO, N, KD, AB, LDAB, RWORK )
      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="ZLASCL.171"></a><a href="zlascl.f.html#ZLASCL.1">ZLASCL</a>( <span class="string">'B'</span>, KD, KD, ONE, SIGMA, N, N, AB, LDAB, INFO )
         ELSE
            CALL <a name="ZLASCL.173"></a><a href="zlascl.f.html#ZLASCL.1">ZLASCL</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="ZHBTRD.177"></a><a href="zhbtrd.f.html#ZHBTRD.1">ZHBTRD</a> to reduce Hermitian band matrix to tridiagonal form.
</span><span class="comment">*</span><span class="comment">
</span>      INDE = 1
      CALL <a name="ZHBTRD.180"></a><a href="zhbtrd.f.html#ZHBTRD.1">ZHBTRD</a>( JOBZ, UPLO, N, KD, AB, LDAB, W, RWORK( INDE ), Z,
     $             LDZ, WORK, IINFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     For eigenvalues only, call <a name="DSTERF.183"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>.  For eigenvectors, call <a name="ZSTEQR.183"></a><a href="zsteqr.f.html#ZSTEQR.1">ZSTEQR</a>.
</span><span class="comment">*</span><span class="comment">
</span>      IF( .NOT.WANTZ ) THEN
         CALL <a name="DSTERF.186"></a><a href="dsterf.f.html#DSTERF.1">DSTERF</a>( N, W, RWORK( INDE ), INFO )
      ELSE
         INDRWK = INDE + N
         CALL <a name="ZSTEQR.189"></a><a href="zsteqr.f.html#ZSTEQR.1">ZSTEQR</a>( JOBZ, N, W, RWORK( INDE ), Z, LDZ,
     $                RWORK( INDRWK ), 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="ZHBEV.206"></a><a href="zhbev.f.html#ZHBEV.1">ZHBEV</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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