dgbcon.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 251 行 · 第 1/2 页

</span><span class="comment">*</span><span class="comment">     Test the input parameters.
</span><span class="comment">*</span><span class="comment">
</span>      INFO = 0
      ONENRM = NORM.EQ.<span class="string">'1'</span> .OR. <a name="LSAME.111"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( NORM, <span class="string">'O'</span> )
      IF( .NOT.ONENRM .AND. .NOT.<a name="LSAME.112"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( NORM, <span class="string">'I'</span> ) ) THEN
         INFO = -1
      ELSE IF( N.LT.0 ) THEN
         INFO = -2
      ELSE IF( KL.LT.0 ) THEN
         INFO = -3
      ELSE IF( KU.LT.0 ) THEN
         INFO = -4
      ELSE IF( LDAB.LT.2*KL+KU+1 ) THEN
         INFO = -6
      ELSE IF( ANORM.LT.ZERO ) THEN
         INFO = -8
      END IF
      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="DGBCON.126"></a><a href="dgbcon.f.html#DGBCON.1">DGBCON</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>      RCOND = ZERO
      IF( N.EQ.0 ) THEN
         RCOND = ONE
         RETURN
      ELSE IF( ANORM.EQ.ZERO ) THEN
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span>      SMLNUM = <a name="DLAMCH.140"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>( <span class="string">'Safe minimum'</span> )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Estimate the norm of inv(A).
</span><span class="comment">*</span><span class="comment">
</span>      AINVNM = ZERO
      NORMIN = <span class="string">'N'</span>
      IF( ONENRM ) THEN
         KASE1 = 1
      ELSE
         KASE1 = 2
      END IF
      KD = KL + KU + 1
      LNOTI = KL.GT.0
      KASE = 0
   10 CONTINUE
      CALL <a name="DLACN2.155"></a><a href="dlacn2.f.html#DLACN2.1">DLACN2</a>( N, WORK( N+1 ), WORK, IWORK, AINVNM, KASE, ISAVE )
      IF( KASE.NE.0 ) THEN
         IF( KASE.EQ.KASE1 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Multiply by inv(L).
</span><span class="comment">*</span><span class="comment">
</span>            IF( LNOTI ) THEN
               DO 20 J = 1, N - 1
                  LM = MIN( KL, N-J )
                  JP = IPIV( J )
                  T = WORK( JP )
                  IF( JP.NE.J ) THEN
                     WORK( JP ) = WORK( J )
                     WORK( J ) = T
                  END IF
                  CALL DAXPY( LM, -T, AB( KD+1, J ), 1, WORK( J+1 ), 1 )
   20          CONTINUE
            END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Multiply by inv(U).
</span><span class="comment">*</span><span class="comment">
</span>            CALL <a name="DLATBS.176"></a><a href="dlatbs.f.html#DLATBS.1">DLATBS</a>( <span class="string">'Upper'</span>, <span class="string">'No transpose'</span>, <span class="string">'Non-unit'</span>, NORMIN, N,
     $                   KL+KU, AB, LDAB, WORK, SCALE, WORK( 2*N+1 ),
     $                   INFO )
         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Multiply by inv(U').
</span><span class="comment">*</span><span class="comment">
</span>            CALL <a name="DLATBS.183"></a><a href="dlatbs.f.html#DLATBS.1">DLATBS</a>( <span class="string">'Upper'</span>, <span class="string">'Transpose'</span>, <span class="string">'Non-unit'</span>, NORMIN, N,
     $                   KL+KU, AB, LDAB, WORK, SCALE, WORK( 2*N+1 ),
     $                   INFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Multiply by inv(L').
</span><span class="comment">*</span><span class="comment">
</span>            IF( LNOTI ) THEN
               DO 30 J = N - 1, 1, -1
                  LM = MIN( KL, N-J )
                  WORK( J ) = WORK( J ) - DDOT( LM, AB( KD+1, J ), 1,
     $                        WORK( J+1 ), 1 )
                  JP = IPIV( J )
                  IF( JP.NE.J ) THEN
                     T = WORK( JP )
                     WORK( JP ) = WORK( J )
                     WORK( J ) = T
                  END IF
   30          CONTINUE
            END IF
         END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Divide X by 1/SCALE if doing so will not cause overflow.
</span><span class="comment">*</span><span class="comment">
</span>         NORMIN = <span class="string">'Y'</span>
         IF( SCALE.NE.ONE ) THEN
            IX = IDAMAX( N, WORK, 1 )
            IF( SCALE.LT.ABS( WORK( IX ) )*SMLNUM .OR. SCALE.EQ.ZERO )
     $         GO TO 40
            CALL <a name="DRSCL.211"></a><a href="drscl.f.html#DRSCL.1">DRSCL</a>( N, SCALE, WORK, 1 )
         END IF
         GO TO 10
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Compute the estimate of the reciprocal condition number.
</span><span class="comment">*</span><span class="comment">
</span>      IF( AINVNM.NE.ZERO )
     $   RCOND = ( ONE / AINVNM ) / ANORM
<span class="comment">*</span><span class="comment">
</span>   40 CONTINUE
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DGBCON.224"></a><a href="dgbcon.f.html#DGBCON.1">DGBCON</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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