dswap.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 93 行

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<pre>
      SUBROUTINE <a name="DSWAP.1"></a><a href="dswap.f.html#DSWAP.1">DSWAP</a>(N,DX,INCX,DY,INCY)
<span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      INTEGER INCX,INCY,N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      DOUBLE PRECISION DX(*),DY(*)
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     interchanges two vectors.
</span><span class="comment">*</span><span class="comment">     uses unrolled loops for increments equal one.
</span><span class="comment">*</span><span class="comment">     jack dongarra, linpack, 3/11/78.
</span><span class="comment">*</span><span class="comment">     modified 12/3/93, array(1) declarations changed to array(*)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      DOUBLE PRECISION DTEMP
      INTEGER I,IX,IY,M,MP1
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC MOD
<span class="comment">*</span><span class="comment">     ..
</span>      IF (N.LE.0) RETURN
      IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">       code for unequal increments or equal increments not equal
</span><span class="comment">*</span><span class="comment">         to 1
</span><span class="comment">*</span><span class="comment">
</span>      IX = 1
      IY = 1
      IF (INCX.LT.0) IX = (-N+1)*INCX + 1
      IF (INCY.LT.0) IY = (-N+1)*INCY + 1
      DO 10 I = 1,N
          DTEMP = DX(IX)
          DX(IX) = DY(IY)
          DY(IY) = DTEMP
          IX = IX + INCX
          IY = IY + INCY
   10 CONTINUE
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">       code for both increments equal to 1
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">       clean-up loop
</span><span class="comment">*</span><span class="comment">
</span>   20 M = MOD(N,3)
      IF (M.EQ.0) GO TO 40
      DO 30 I = 1,M
          DTEMP = DX(I)
          DX(I) = DY(I)
          DY(I) = DTEMP
   30 CONTINUE
      IF (N.LT.3) RETURN
   40 MP1 = M + 1
      DO 50 I = MP1,N,3
          DTEMP = DX(I)
          DX(I) = DY(I)
          DY(I) = DTEMP
          DTEMP = DX(I+1)
          DX(I+1) = DY(I+1)
          DY(I+1) = DTEMP
          DTEMP = DX(I+2)
          DX(I+2) = DY(I+2)
          DY(I+2) = DTEMP
   50 CONTINUE
      RETURN
      END

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