subroutine classq (N, X, INCX, SCALE, SUMSQ)
CLASSQ updates a sum of squares represented in scaled form.
CLASSQ updates a sum of squares represented in scaled form.
Purpose:
CLASSQ returns the values scl and ssq such that
( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
where x( i ) = abs( X( 1 + ( i - 1 )*INCX ) ). The value of sumsq is
assumed to be at least unity and the value of ssq will then satisfy
1.0 .le. ssq .le. ( sumsq + 2*n ).
scale is assumed to be non-negative and scl returns the value
scl = max( scale, abs( real( x( i ) ) ), abs( aimag( x( i ) ) ) ),
i
scale and sumsq must be supplied in SCALE and SUMSQ respectively.
SCALE and SUMSQ are overwritten by scl and ssq respectively.
The routine makes only one pass through the vector X.
Parameters:
N is INTEGER
The number of elements to be used from the vector X.
X
X is COMPLEX array, dimension (N)
The vector x as described above.
x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
INCX
INCX is INTEGER
The increment between successive values of the vector X.
INCX > 0.
SCALE
SCALE is REAL
On entry, the value scale in the equation above.
On exit, SCALE is overwritten with the value scl .
SUMSQ
SUMSQ is REAL
On entry, the value sumsq in the equation above.
On exit, SUMSQ is overwritten with the value ssq .
Author:
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
Definition at line 108 of file classq.f.
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