LAPACK  3.4.2 LAPACK: Linear Algebra PACKage
zlassq.f File Reference

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Functions/Subroutines

subroutine zlassq (N, X, INCX, SCALE, SUMSQ)
ZLASSQ updates a sum of squares represented in scaled form.

Function/Subroutine Documentation

 subroutine zlassq ( integer N, complex*16, dimension( * ) X, integer INCX, double precision SCALE, double precision SUMSQ )

ZLASSQ updates a sum of squares represented in scaled form.

Purpose:
``` ZLASSQ 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:
 [in] N ``` N is INTEGER The number of elements to be used from the vector X.``` [in] X ``` X is COMPLEX*16 array, dimension (N) The vector x as described above. x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.``` [in] INCX ``` INCX is INTEGER The increment between successive values of the vector X. INCX > 0.``` [in,out] SCALE ``` SCALE is DOUBLE PRECISION On entry, the value scale in the equation above. On exit, SCALE is overwritten with the value scl .``` [in,out] SUMSQ ``` SUMSQ is DOUBLE PRECISION On entry, the value sumsq in the equation above. On exit, SUMSQ is overwritten with the value ssq .```
Date:
September 2012

Definition at line 107 of file zlassq.f.

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