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来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 293 行 · 第 1/2 页

     $                   SMLNUM
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Functions ..
</span>      LOGICAL            <a name="LSAME.132"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      REAL               <a name="SLAMCH.133"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>, <a name="SLANSB.133"></a><a href="slansb.f.html#SLANSB.1">SLANSB</a>
      EXTERNAL           <a name="LSAME.134"></a><a href="lsame.f.html#LSAME.1">LSAME</a>, <a name="SLAMCH.134"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>, <a name="SLANSB.134"></a><a href="slansb.f.html#SLANSB.1">SLANSB</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           SGEMM, <a name="SLACPY.137"></a><a href="slacpy.f.html#SLACPY.1">SLACPY</a>, <a name="SLASCL.137"></a><a href="slascl.f.html#SLASCL.1">SLASCL</a>, <a name="SSBTRD.137"></a><a href="ssbtrd.f.html#SSBTRD.1">SSBTRD</a>, SSCAL, <a name="SSTEDC.137"></a><a href="sstedc.f.html#SSTEDC.1">SSTEDC</a>,
     $                   <a name="SSTERF.138"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a>, <a name="XERBLA.138"></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.147"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'V'</span> )
      LOWER = <a name="LSAME.148"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'L'</span> )
      LQUERY = ( LWORK.EQ.-1 .OR. LIWORK.EQ.-1 )
<span class="comment">*</span><span class="comment">
</span>      INFO = 0
      IF( N.LE.1 ) THEN
         LIWMIN = 1
         LWMIN = 1
      ELSE
         IF( WANTZ ) THEN
            LIWMIN = 3 + 5*N
            LWMIN = 1 + 5*N + 2*N**2
         ELSE
            LIWMIN = 1
            LWMIN = 2*N
         END IF
      END IF
      IF( .NOT.( WANTZ .OR. <a name="LSAME.164"></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.166"></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.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 = -11
         ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -13
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.190"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="SSBEVD.190"></a><a href="ssbevd.f.html#SSBEVD.1">SSBEVD</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
         W( 1 ) = AB( 1, 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="SLAMCH.210"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>( <span class="string">'Safe minimum'</span> )
      EPS = <a name="SLAMCH.211"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</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="SLANSB.219"></a><a href="slansb.f.html#SLANSB.1">SLANSB</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="SLASCL.230"></a><a href="slascl.f.html#SLASCL.1">SLASCL</a>( <span class="string">'B'</span>, KD, KD, ONE, SIGMA, N, N, AB, LDAB, INFO )
         ELSE
            CALL <a name="SLASCL.232"></a><a href="slascl.f.html#SLASCL.1">SLASCL</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="SSBTRD.236"></a><a href="ssbtrd.f.html#SSBTRD.1">SSBTRD</a> to reduce symmetric band matrix to tridiagonal form.
</span><span class="comment">*</span><span class="comment">
</span>      INDE = 1
      INDWRK = INDE + N
      INDWK2 = INDWRK + N*N
      LLWRK2 = LWORK - INDWK2 + 1
      CALL <a name="SSBTRD.242"></a><a href="ssbtrd.f.html#SSBTRD.1">SSBTRD</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="SSTERF.245"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a>.  For eigenvectors, call <a name="SSTEDC.245"></a><a href="sstedc.f.html#SSTEDC.1">SSTEDC</a>.
</span><span class="comment">*</span><span class="comment">
</span>      IF( .NOT.WANTZ ) THEN
         CALL <a name="SSTERF.248"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a>( N, W, WORK( INDE ), INFO )
      ELSE
         CALL <a name="SSTEDC.250"></a><a href="sstedc.f.html#SSTEDC.1">SSTEDC</a>( <span class="string">'I'</span>, N, W, WORK( INDE ), WORK( INDWRK ), N,
     $                WORK( INDWK2 ), LLWRK2, IWORK, LIWORK, INFO )
         CALL SGEMM( <span class="string">'N'</span>, <span class="string">'N'</span>, N, N, N, ONE, Z, LDZ, WORK( INDWRK ), N,
     $               ZERO, WORK( INDWK2 ), N )
         CALL <a name="SLACPY.254"></a><a href="slacpy.f.html#SLACPY.1">SLACPY</a>( <span class="string">'A'</span>, N, N, WORK( INDWK2 ), N, Z, LDZ )
      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 SSCAL( N, ONE / SIGMA, W, 1 )
<span class="comment">*</span><span class="comment">
</span>      WORK( 1 ) = LWMIN
      IWORK( 1 ) = LIWMIN
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="SSBEVD.266"></a><a href="ssbevd.f.html#SSBEVD.1">SSBEVD</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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