dgbequ.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 264 行 · 第 1/2 页

         INFO = -3
      ELSE IF( KU.LT.0 ) THEN
         INFO = -4
      ELSE IF( LDAB.LT.KL+KU+1 ) THEN
         INFO = -6
      END IF
      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.121"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="DGBEQU.121"></a><a href="dgbequ.f.html#DGBEQU.1">DGBEQU</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( M.EQ.0 .OR. N.EQ.0 ) THEN
         ROWCND = ONE
         COLCND = ONE
         AMAX = ZERO
         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>      SMLNUM = <a name="DLAMCH.136"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>( <span class="string">'S'</span> )
      BIGNUM = ONE / SMLNUM
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Compute row scale factors.
</span><span class="comment">*</span><span class="comment">
</span>      DO 10 I = 1, M
         R( I ) = ZERO
   10 CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Find the maximum element in each row.
</span><span class="comment">*</span><span class="comment">
</span>      KD = KU + 1
      DO 30 J = 1, N
         DO 20 I = MAX( J-KU, 1 ), MIN( J+KL, M )
            R( I ) = MAX( R( I ), ABS( AB( KD+I-J, J ) ) )
   20    CONTINUE
   30 CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Find the maximum and minimum scale factors.
</span><span class="comment">*</span><span class="comment">
</span>      RCMIN = BIGNUM
      RCMAX = ZERO
      DO 40 I = 1, M
         RCMAX = MAX( RCMAX, R( I ) )
         RCMIN = MIN( RCMIN, R( I ) )
   40 CONTINUE
      AMAX = RCMAX
<span class="comment">*</span><span class="comment">
</span>      IF( RCMIN.EQ.ZERO ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Find the first zero scale factor and return an error code.
</span><span class="comment">*</span><span class="comment">
</span>         DO 50 I = 1, M
            IF( R( I ).EQ.ZERO ) THEN
               INFO = I
               RETURN
            END IF
   50    CONTINUE
      ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Invert the scale factors.
</span><span class="comment">*</span><span class="comment">
</span>         DO 60 I = 1, M
            R( I ) = ONE / MIN( MAX( R( I ), SMLNUM ), BIGNUM )
   60    CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Compute ROWCND = min(R(I)) / max(R(I))
</span><span class="comment">*</span><span class="comment">
</span>         ROWCND = MAX( RCMIN, SMLNUM ) / MIN( RCMAX, BIGNUM )
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Compute column scale factors
</span><span class="comment">*</span><span class="comment">
</span>      DO 70 J = 1, N
         C( J ) = ZERO
   70 CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Find the maximum element in each column,
</span><span class="comment">*</span><span class="comment">     assuming the row scaling computed above.
</span><span class="comment">*</span><span class="comment">
</span>      KD = KU + 1
      DO 90 J = 1, N
         DO 80 I = MAX( J-KU, 1 ), MIN( J+KL, M )
            C( J ) = MAX( C( J ), ABS( AB( KD+I-J, J ) )*R( I ) )
   80    CONTINUE
   90 CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Find the maximum and minimum scale factors.
</span><span class="comment">*</span><span class="comment">
</span>      RCMIN = BIGNUM
      RCMAX = ZERO
      DO 100 J = 1, N
         RCMIN = MIN( RCMIN, C( J ) )
         RCMAX = MAX( RCMAX, C( J ) )
  100 CONTINUE
<span class="comment">*</span><span class="comment">
</span>      IF( RCMIN.EQ.ZERO ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Find the first zero scale factor and return an error code.
</span><span class="comment">*</span><span class="comment">
</span>         DO 110 J = 1, N
            IF( C( J ).EQ.ZERO ) THEN
               INFO = M + J
               RETURN
            END IF
  110    CONTINUE
      ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Invert the scale factors.
</span><span class="comment">*</span><span class="comment">
</span>         DO 120 J = 1, N
            C( J ) = ONE / MIN( MAX( C( J ), SMLNUM ), BIGNUM )
  120    CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Compute COLCND = min(C(J)) / max(C(J))
</span><span class="comment">*</span><span class="comment">
</span>         COLCND = MAX( RCMIN, SMLNUM ) / MIN( RCMAX, BIGNUM )
      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="DGBEQU.237"></a><a href="dgbequ.f.html#DGBEQU.1">DGBEQU</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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