zlassq.f.html
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SUBROUTINE <a name="ZLASSQ.1"></a><a href="zlassq.f.html#ZLASSQ.1">ZLASSQ</a>( N, X, INCX, SCALE, SUMSQ )
<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> INTEGER INCX, N
DOUBLE PRECISION SCALE, SUMSQ
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Array Arguments ..
</span> COMPLEX*16 X( * )
<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="ZLASSQ.18"></a><a href="zlassq.f.html#ZLASSQ.1">ZLASSQ</a> returns the values scl and ssq such that
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> ( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> where x( i ) = abs( X( 1 + ( i - 1 )*INCX ) ). The value of sumsq is
</span><span class="comment">*</span><span class="comment"> assumed to be at least unity and the value of ssq will then satisfy
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> 1.0 .le. ssq .le. ( sumsq + 2*n ).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> scale is assumed to be non-negative and scl returns the value
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> scl = max( scale, abs( real( x( i ) ) ), abs( aimag( x( i ) ) ) ),
</span><span class="comment">*</span><span class="comment"> i
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> scale and sumsq must be supplied in SCALE and SUMSQ respectively.
</span><span class="comment">*</span><span class="comment"> SCALE and SUMSQ are overwritten by scl and ssq respectively.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> The routine makes only one pass through the vector X.
</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"> N (input) INTEGER
</span><span class="comment">*</span><span class="comment"> The number of elements to be used from the vector X.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> X (input) COMPLEX*16 array, dimension (N)
</span><span class="comment">*</span><span class="comment"> The vector x as described above.
</span><span class="comment">*</span><span class="comment"> x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> INCX (input) INTEGER
</span><span class="comment">*</span><span class="comment"> The increment between successive values of the vector X.
</span><span class="comment">*</span><span class="comment"> INCX > 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> SCALE (input/output) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment"> On entry, the value scale in the equation above.
</span><span class="comment">*</span><span class="comment"> On exit, SCALE is overwritten with the value scl .
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> SUMSQ (input/output) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment"> On entry, the value sumsq in the equation above.
</span><span class="comment">*</span><span class="comment"> On exit, SUMSQ is overwritten with the value ssq .
</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"> .. Parameters ..
</span> DOUBLE PRECISION ZERO
PARAMETER ( ZERO = 0.0D+0 )
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Local Scalars ..
</span> INTEGER IX
DOUBLE PRECISION TEMP1
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Intrinsic Functions ..
</span> INTRINSIC ABS, DBLE, DIMAG
<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( N.GT.0 ) THEN
DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
IF( DBLE( X( IX ) ).NE.ZERO ) THEN
TEMP1 = ABS( DBLE( X( IX ) ) )
IF( SCALE.LT.TEMP1 ) THEN
SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
SCALE = TEMP1
ELSE
SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
END IF
END IF
IF( DIMAG( X( IX ) ).NE.ZERO ) THEN
TEMP1 = ABS( DIMAG( X( IX ) ) )
IF( SCALE.LT.TEMP1 ) THEN
SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
SCALE = TEMP1
ELSE
SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
END IF
END IF
10 CONTINUE
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="ZLASSQ.99"></a><a href="zlassq.f.html#ZLASSQ.1">ZLASSQ</a>
</span><span class="comment">*</span><span class="comment">
</span> END
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