dgemv.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 286 行 · 第 1/2 页

     +    .NOT.<a name="LSAME.125"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(TRANS,<span class="string">'C'</span>)) THEN
          INFO = 1
      ELSE IF (M.LT.0) THEN
          INFO = 2
      ELSE IF (N.LT.0) THEN
          INFO = 3
      ELSE IF (LDA.LT.MAX(1,M)) 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.139"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>(<span class="string">'<a name="DGEMV.139"></a><a href="dgemv.f.html#DGEMV.1">DGEMV</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) .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  LENX  and  LENY, the lengths of the vectors x and y, and set
</span><span class="comment">*</span><span class="comment">     up the start points in  X  and  Y.
</span><span class="comment">*</span><span class="comment">
</span>      IF (<a name="LSAME.151"></a><a href="lsame.f.html#LSAME.1">LSAME</a>(TRANS,<span class="string">'N'</span>)) THEN
          LENX = N
          LENY = M
      ELSE
          LENX = M
          LENY = N
      END IF
      IF (INCX.GT.0) THEN
          KX = 1
      ELSE
          KX = 1 - (LENX-1)*INCX
      END IF
      IF (INCY.GT.0) THEN
          KY = 1
      ELSE
          KY = 1 - (LENY-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 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><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,LENY
                      Y(I) = ZERO
   10             CONTINUE
              ELSE
                  DO 20 I = 1,LENY
                      Y(I) = BETA*Y(I)
   20             CONTINUE
              END IF
          ELSE
              IY = KY
              IF (BETA.EQ.ZERO) THEN
                  DO 30 I = 1,LENY
                      Y(IY) = ZERO
                      IY = IY + INCY
   30             CONTINUE
              ELSE
                  DO 40 I = 1,LENY
                      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.201"></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  y := alpha*A*x + y.
</span><span class="comment">*</span><span class="comment">
</span>          JX = KX
          IF (INCY.EQ.1) THEN
              DO 60 J = 1,N
                  IF (X(JX).NE.ZERO) THEN
                      TEMP = ALPHA*X(JX)
                      DO 50 I = 1,M
                          Y(I) = Y(I) + TEMP*A(I,J)
   50                 CONTINUE
                  END IF
                  JX = JX + INCX
   60         CONTINUE
          ELSE
              DO 80 J = 1,N
                  IF (X(JX).NE.ZERO) THEN
                      TEMP = ALPHA*X(JX)
                      IY = KY
                      DO 70 I = 1,M
                          Y(IY) = Y(IY) + TEMP*A(I,J)
                          IY = IY + INCY
   70                 CONTINUE
                  END IF
                  JX = JX + INCX
   80         CONTINUE
          END IF
      ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Form  y := alpha*A'*x + y.
</span><span class="comment">*</span><span class="comment">
</span>          JY = KY
          IF (INCX.EQ.1) THEN
              DO 100 J = 1,N
                  TEMP = ZERO
                  DO 90 I = 1,M
                      TEMP = TEMP + A(I,J)*X(I)
   90             CONTINUE
                  Y(JY) = Y(JY) + ALPHA*TEMP
                  JY = JY + INCY
  100         CONTINUE
          ELSE
              DO 120 J = 1,N
                  TEMP = ZERO
                  IX = KX
                  DO 110 I = 1,M
                      TEMP = TEMP + A(I,J)*X(IX)
                      IX = IX + INCX
  110             CONTINUE
                  Y(JY) = Y(JY) + ALPHA*TEMP
                  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="DGEMV.259"></a><a href="dgemv.f.html#DGEMV.1">DGEMV</a> .
</span><span class="comment">*</span><span class="comment">
</span>      END

</pre>

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