dasum.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 80 行

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<pre>
      DOUBLE PRECISION FUNCTION <a name="DASUM.1"></a><a href="dasum.f.html#DASUM.1">DASUM</a>(N,DX,INCX)
<span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      INTEGER INCX,N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      DOUBLE PRECISION DX(*)
<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">     takes the sum of the absolute values.
</span><span class="comment">*</span><span class="comment">     jack dongarra, linpack, 3/11/78.
</span><span class="comment">*</span><span class="comment">     modified 3/93 to return if incx .le. 0.
</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,M,MP1,NINCX
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC DABS,MOD
<span class="comment">*</span><span class="comment">     ..
</span>      <a name="DASUM.25"></a><a href="dasum.f.html#DASUM.1">DASUM</a> = 0.0d0
      DTEMP = 0.0d0
      IF (N.LE.0 .OR. INCX.LE.0) RETURN
      IF (INCX.EQ.1) GO TO 20
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        code for increment not equal to 1
</span><span class="comment">*</span><span class="comment">
</span>      NINCX = N*INCX
      DO 10 I = 1,NINCX,INCX
          DTEMP = DTEMP + DABS(DX(I))
   10 CONTINUE
      <a name="DASUM.36"></a><a href="dasum.f.html#DASUM.1">DASUM</a> = DTEMP
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        code for increment 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,6)
      IF (M.EQ.0) GO TO 40
      DO 30 I = 1,M
          DTEMP = DTEMP + DABS(DX(I))
   30 CONTINUE
      IF (N.LT.6) GO TO 60
   40 MP1 = M + 1
      DO 50 I = MP1,N,6
          DTEMP = DTEMP + DABS(DX(I)) + DABS(DX(I+1)) + DABS(DX(I+2)) +
     +            DABS(DX(I+3)) + DABS(DX(I+4)) + DABS(DX(I+5))
   50 CONTINUE
   60 <a name="DASUM.55"></a><a href="dasum.f.html#DASUM.1">DASUM</a> = DTEMP
      RETURN
      END

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