dtbcon.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 227 行 · 第 1/2 页

      INTEGER            IDAMAX
      DOUBLE PRECISION   <a name="DLAMCH.97"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>, <a name="DLANTB.97"></a><a href="dlantb.f.html#DLANTB.1">DLANTB</a>
      EXTERNAL           <a name="LSAME.98"></a><a href="lsame.f.html#LSAME.1">LSAME</a>, IDAMAX, <a name="DLAMCH.98"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>, <a name="DLANTB.98"></a><a href="dlantb.f.html#DLANTB.1">DLANTB</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="DLACN2.101"></a><a href="dlacn2.f.html#DLACN2.1">DLACN2</a>, <a name="DLATBS.101"></a><a href="dlatbs.f.html#DLATBS.1">DLATBS</a>, <a name="DRSCL.101"></a><a href="drscl.f.html#DRSCL.1">DRSCL</a>, <a name="XERBLA.101"></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          ABS, DBLE, MAX
<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>      INFO = 0
      UPPER = <a name="LSAME.111"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'U'</span> )
      ONENRM = NORM.EQ.<span class="string">'1'</span> .OR. <a name="LSAME.112"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( NORM, <span class="string">'O'</span> )
      NOUNIT = <a name="LSAME.113"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( DIAG, <span class="string">'N'</span> )
<span class="comment">*</span><span class="comment">
</span>      IF( .NOT.ONENRM .AND. .NOT.<a name="LSAME.115"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( NORM, <span class="string">'I'</span> ) ) THEN
         INFO = -1
      ELSE IF( .NOT.UPPER .AND. .NOT.<a name="LSAME.117"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'L'</span> ) ) THEN
         INFO = -2
      ELSE IF( .NOT.NOUNIT .AND. .NOT.<a name="LSAME.119"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( DIAG, <span class="string">'U'</span> ) ) THEN
         INFO = -3
      ELSE IF( N.LT.0 ) THEN
         INFO = -4
      ELSE IF( KD.LT.0 ) THEN
         INFO = -5
      ELSE IF( LDAB.LT.KD+1 ) THEN
         INFO = -7
      END IF
      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="DTBCON.129"></a><a href="dtbcon.f.html#DTBCON.1">DTBCON</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 ) THEN
         RCOND = ONE
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span>      RCOND = ZERO
      SMLNUM = <a name="DLAMCH.141"></a><a href="dlamch.f.html#DLAMCH.1">DLAMCH</a>( <span class="string">'Safe minimum'</span> )*DBLE( MAX( 1, N ) )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Compute the norm of the triangular matrix A.
</span><span class="comment">*</span><span class="comment">
</span>      ANORM = <a name="DLANTB.145"></a><a href="dlantb.f.html#DLANTB.1">DLANTB</a>( NORM, UPLO, DIAG, N, KD, AB, LDAB, WORK )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Continue only if ANORM &gt; 0.
</span><span class="comment">*</span><span class="comment">
</span>      IF( ANORM.GT.ZERO ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Estimate the norm of the inverse of 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
         KASE = 0
   10    CONTINUE
         CALL <a name="DLACN2.162"></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(A).
</span><span class="comment">*</span><span class="comment">
</span>               CALL <a name="DLATBS.168"></a><a href="dlatbs.f.html#DLATBS.1">DLATBS</a>( UPLO, <span class="string">'No transpose'</span>, DIAG, NORMIN, N, KD,
     $                      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(A').
</span><span class="comment">*</span><span class="comment">
</span>               CALL <a name="DLATBS.174"></a><a href="dlatbs.f.html#DLATBS.1">DLATBS</a>( UPLO, <span class="string">'Transpose'</span>, DIAG, NORMIN, N, KD, AB,
     $                      LDAB, WORK, SCALE, WORK( 2*N+1 ), INFO )
            END IF
            NORMIN = <span class="string">'Y'</span>
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Multiply by 1/SCALE if doing so will not cause overflow.
</span><span class="comment">*</span><span class="comment">
</span>            IF( SCALE.NE.ONE ) THEN
               IX = IDAMAX( N, WORK, 1 )
               XNORM = ABS( WORK( IX ) )
               IF( SCALE.LT.XNORM*SMLNUM .OR. SCALE.EQ.ZERO )
     $            GO TO 20
               CALL <a name="DRSCL.186"></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 / ANORM ) / AINVNM
      END IF
<span class="comment">*</span><span class="comment">
</span>   20 CONTINUE
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DTBCON.200"></a><a href="dtbcon.f.html#DTBCON.1">DTBCON</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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