dtrsv.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 306 行 · 第 1/2 页

          INFO = 4
      ELSE IF (LDA.LT.MAX(1,N)) THEN
          INFO = 6
      ELSE IF (INCX.EQ.0) THEN
          INFO = 8
      END IF
      IF (INFO.NE.0) THEN
          CALL <a name="XERBLA.142"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>(<span class="string">'<a name="DTRSV.142"></a><a href="dtrsv.f.html#DTRSV.1">DTRSV</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>      NOUNIT = <a name="LSAME.150"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(DIAG,<span class="string">'N'</span>)
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Set up the start point in X if the increment is not unity. This
</span><span class="comment">*</span><span class="comment">     will be  ( N - 1 )*INCX  too small for descending loops.
</span><span class="comment">*</span><span class="comment">
</span>      IF (INCX.LE.0) THEN
          KX = 1 - (N-1)*INCX
      ELSE IF (INCX.NE.1) THEN
          KX = 1
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Start the operations. In this version the elements of A are
</span><span class="comment">*</span><span class="comment">     accessed sequentially with one pass through A.
</span><span class="comment">*</span><span class="comment">
</span>      IF (<a name="LSAME.164"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(TRANS,<span class="string">'N'</span>)) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Form  x := inv( A )*x.
</span><span class="comment">*</span><span class="comment">
</span>          IF (<a name="LSAME.168"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(UPLO,<span class="string">'U'</span>)) THEN
              IF (INCX.EQ.1) THEN
                  DO 20 J = N,1,-1
                      IF (X(J).NE.ZERO) THEN
                          IF (NOUNIT) X(J) = X(J)/A(J,J)
                          TEMP = X(J)
                          DO 10 I = J - 1,1,-1
                              X(I) = X(I) - TEMP*A(I,J)
   10                     CONTINUE
                      END IF
   20             CONTINUE
              ELSE
                  JX = KX + (N-1)*INCX
                  DO 40 J = N,1,-1
                      IF (X(JX).NE.ZERO) THEN
                          IF (NOUNIT) X(JX) = X(JX)/A(J,J)
                          TEMP = X(JX)
                          IX = JX
                          DO 30 I = J - 1,1,-1
                              IX = IX - INCX
                              X(IX) = X(IX) - TEMP*A(I,J)
   30                     CONTINUE
                      END IF
                      JX = JX - INCX
   40             CONTINUE
              END IF
          ELSE
              IF (INCX.EQ.1) THEN
                  DO 60 J = 1,N
                      IF (X(J).NE.ZERO) THEN
                          IF (NOUNIT) X(J) = X(J)/A(J,J)
                          TEMP = X(J)
                          DO 50 I = J + 1,N
                              X(I) = X(I) - TEMP*A(I,J)
   50                     CONTINUE
                      END IF
   60             CONTINUE
              ELSE
                  JX = KX
                  DO 80 J = 1,N
                      IF (X(JX).NE.ZERO) THEN
                          IF (NOUNIT) X(JX) = X(JX)/A(J,J)
                          TEMP = X(JX)
                          IX = JX
                          DO 70 I = J + 1,N
                              IX = IX + INCX
                              X(IX) = X(IX) - TEMP*A(I,J)
   70                     CONTINUE
                      END IF
                      JX = JX + INCX
   80             CONTINUE
              END IF
          END IF
      ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Form  x := inv( A' )*x.
</span><span class="comment">*</span><span class="comment">
</span>          IF (<a name="LSAME.225"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(UPLO,<span class="string">'U'</span>)) THEN
              IF (INCX.EQ.1) THEN
                  DO 100 J = 1,N
                      TEMP = X(J)
                      DO 90 I = 1,J - 1
                          TEMP = TEMP - A(I,J)*X(I)
   90                 CONTINUE
                      IF (NOUNIT) TEMP = TEMP/A(J,J)
                      X(J) = TEMP
  100             CONTINUE
              ELSE
                  JX = KX
                  DO 120 J = 1,N
                      TEMP = X(JX)
                      IX = KX
                      DO 110 I = 1,J - 1
                          TEMP = TEMP - A(I,J)*X(IX)
                          IX = IX + INCX
  110                 CONTINUE
                      IF (NOUNIT) TEMP = TEMP/A(J,J)
                      X(JX) = TEMP
                      JX = JX + INCX
  120             CONTINUE
              END IF
          ELSE
              IF (INCX.EQ.1) THEN
                  DO 140 J = N,1,-1
                      TEMP = X(J)
                      DO 130 I = N,J + 1,-1
                          TEMP = TEMP - A(I,J)*X(I)
  130                 CONTINUE
                      IF (NOUNIT) TEMP = TEMP/A(J,J)
                      X(J) = TEMP
  140             CONTINUE
              ELSE
                  KX = KX + (N-1)*INCX
                  JX = KX
                  DO 160 J = N,1,-1
                      TEMP = X(JX)
                      IX = KX
                      DO 150 I = N,J + 1,-1
                          TEMP = TEMP - A(I,J)*X(IX)
                          IX = IX - INCX
  150                 CONTINUE
                      IF (NOUNIT) TEMP = TEMP/A(J,J)
                      X(JX) = TEMP
                      JX = JX - INCX
  160             CONTINUE
              END IF
          END IF
      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="DTRSV.279"></a><a href="dtrsv.f.html#DTRSV.1">DTRSV</a> .
</span><span class="comment">*</span><span class="comment">
</span>      END

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