classq-f(3)

classq.f –

Synopsis

Functions/Subroutines

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

Function/Subroutine Documentation

subroutine classq (integerN, complex, dimension( * )X, integerINCX, realSCALE, realSUMSQ)

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 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 Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 107 of file classq.f.

Author

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