dladiv.f.html
来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 85 行
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SUBROUTINE <a name="DLADIV.1"></a><a href="dladiv.f.html#DLADIV.1">DLADIV</a>( A, B, C, D, P, Q )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> -- LAPACK auxiliary routine (version 3.1) --
</span><span class="comment">*</span><span class="comment"> Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment"> November 2006
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> .. Scalar Arguments ..
</span> DOUBLE PRECISION A, B, C, D, P, Q
<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"> <a name="DLADIV.14"></a><a href="dladiv.f.html#DLADIV.1">DLADIV</a> performs complex division in real arithmetic
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> a + i*b
</span><span class="comment">*</span><span class="comment"> p + i*q = ---------
</span><span class="comment">*</span><span class="comment"> c + i*d
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> The algorithm is due to Robert L. Smith and can be found
</span><span class="comment">*</span><span class="comment"> in D. Knuth, The art of Computer Programming, Vol.2, p.195
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> Arguments
</span><span class="comment">*</span><span class="comment"> =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> A (input) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment"> B (input) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment"> C (input) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment"> D (input) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment"> The scalars a, b, c, and d in the above expression.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> P (output) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment"> Q (output) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment"> The scalars p and q in the above expression.
</span><span class="comment">*</span><span class="comment">
</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 E, F
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Intrinsic Functions ..
</span> INTRINSIC ABS
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span> IF( ABS( D ).LT.ABS( C ) ) THEN
E = D / C
F = C + D*E
P = ( A+B*E ) / F
Q = ( B-A*E ) / F
ELSE
E = C / D
F = D + C*E
P = ( B+A*E ) / F
Q = ( -A+B*E ) / F
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="DLADIV.60"></a><a href="dladiv.f.html#DLADIV.1">DLADIV</a>
</span><span class="comment">*</span><span class="comment">
</span> END
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