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来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 328 行 · 第 1/2 页

</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC MAX,MIN
<span class="comment">*</span><span class="comment">     ..
</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
      IF (.NOT.<a name="LSAME.153"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(UPLO,<span class="string">'U'</span>) .AND. .NOT.<a name="LSAME.153"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(UPLO,<span class="string">'L'</span>)) THEN
          INFO = 1
      ELSE IF (N.LT.0) THEN
          INFO = 2
      ELSE IF (K.LT.0) THEN
          INFO = 3
      ELSE IF (LDA.LT. (K+1)) THEN
          INFO = 6
      ELSE IF (INCX.EQ.0) THEN
          INFO = 8
      ELSE IF (INCY.EQ.0) THEN
          INFO = 11
      END IF
      IF (INFO.NE.0) THEN
          CALL <a name="XERBLA.167"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>(<span class="string">'<a name="DSBMV.167"></a><a href="dsbmv.f.html#DSBMV.1">DSBMV</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) .OR. ((ALPHA.EQ.ZERO).AND. (BETA.EQ.ONE))) RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Set up the start points in  X  and  Y.
</span><span class="comment">*</span><span class="comment">
</span>      IF (INCX.GT.0) THEN
          KX = 1
      ELSE
          KX = 1 - (N-1)*INCX
      END IF
      IF (INCY.GT.0) THEN
          KY = 1
      ELSE
          KY = 1 - (N-1)*INCY
      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 the array A
</span><span class="comment">*</span><span class="comment">     are accessed sequentially with one pass through A.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     First form  y := beta*y.
</span><span class="comment">*</span><span class="comment">
</span>      IF (BETA.NE.ONE) THEN
          IF (INCY.EQ.1) THEN
              IF (BETA.EQ.ZERO) THEN
                  DO 10 I = 1,N
                      Y(I) = ZERO
   10             CONTINUE
              ELSE
                  DO 20 I = 1,N
                      Y(I) = BETA*Y(I)
   20             CONTINUE
              END IF
          ELSE
              IY = KY
              IF (BETA.EQ.ZERO) THEN
                  DO 30 I = 1,N
                      Y(IY) = ZERO
                      IY = IY + INCY
   30             CONTINUE
              ELSE
                  DO 40 I = 1,N
                      Y(IY) = BETA*Y(IY)
                      IY = IY + INCY
   40             CONTINUE
              END IF
          END IF
      END IF
      IF (ALPHA.EQ.ZERO) RETURN
      IF (<a name="LSAME.220"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(UPLO,<span class="string">'U'</span>)) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Form  y  when upper triangle of A is stored.
</span><span class="comment">*</span><span class="comment">
</span>          KPLUS1 = K + 1
          IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN
              DO 60 J = 1,N
                  TEMP1 = ALPHA*X(J)
                  TEMP2 = ZERO
                  L = KPLUS1 - J
                  DO 50 I = MAX(1,J-K),J - 1
                      Y(I) = Y(I) + TEMP1*A(L+I,J)
                      TEMP2 = TEMP2 + A(L+I,J)*X(I)
   50             CONTINUE
                  Y(J) = Y(J) + TEMP1*A(KPLUS1,J) + ALPHA*TEMP2
   60         CONTINUE
          ELSE
              JX = KX
              JY = KY
              DO 80 J = 1,N
                  TEMP1 = ALPHA*X(JX)
                  TEMP2 = ZERO
                  IX = KX
                  IY = KY
                  L = KPLUS1 - J
                  DO 70 I = MAX(1,J-K),J - 1
                      Y(IY) = Y(IY) + TEMP1*A(L+I,J)
                      TEMP2 = TEMP2 + A(L+I,J)*X(IX)
                      IX = IX + INCX
                      IY = IY + INCY
   70             CONTINUE
                  Y(JY) = Y(JY) + TEMP1*A(KPLUS1,J) + ALPHA*TEMP2
                  JX = JX + INCX
                  JY = JY + INCY
                  IF (J.GT.K) THEN
                      KX = KX + INCX
                      KY = KY + INCY
                  END IF
   80         CONTINUE
          END IF
      ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Form  y  when lower triangle of A is stored.
</span><span class="comment">*</span><span class="comment">
</span>          IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN
              DO 100 J = 1,N
                  TEMP1 = ALPHA*X(J)
                  TEMP2 = ZERO
                  Y(J) = Y(J) + TEMP1*A(1,J)
                  L = 1 - J
                  DO 90 I = J + 1,MIN(N,J+K)
                      Y(I) = Y(I) + TEMP1*A(L+I,J)
                      TEMP2 = TEMP2 + A(L+I,J)*X(I)
   90             CONTINUE
                  Y(J) = Y(J) + ALPHA*TEMP2
  100         CONTINUE
          ELSE
              JX = KX
              JY = KY
              DO 120 J = 1,N
                  TEMP1 = ALPHA*X(JX)
                  TEMP2 = ZERO
                  Y(JY) = Y(JY) + TEMP1*A(1,J)
                  L = 1 - J
                  IX = JX
                  IY = JY
                  DO 110 I = J + 1,MIN(N,J+K)
                      IX = IX + INCX
                      IY = IY + INCY
                      Y(IY) = Y(IY) + TEMP1*A(L+I,J)
                      TEMP2 = TEMP2 + A(L+I,J)*X(IX)
  110             CONTINUE
                  Y(JY) = Y(JY) + ALPHA*TEMP2
                  JX = JX + INCX
                  JY = JY + INCY
  120         CONTINUE
          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="DSBMV.301"></a><a href="dsbmv.f.html#DSBMV.1">DSBMV</a> .
</span><span class="comment">*</span><span class="comment">
</span>      END

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