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.

Download ZLASSQ + dependencies [TGZ] [ZIP] [TXT]

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 .

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 107 of file zlassq.f.

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