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