dlassq.f (3)

Functions/Subroutines

subroutine dlassq (N, X, INCX, SCALE, SUMSQ)

DLASSQ updates a sum of squares represented in scaled form.

subroutine dlassq (integerN, double precision, dimension( * )X, integerINCX, double precisionSCALE, double precisionSUMSQ)

DLASSQ updates a sum of squares represented in scaled form.

Purpose:

 DLASSQ  returns the values  scl  and  smsq  such that

    ( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,

 where  x( i ) = X( 1 + ( i - 1 )*INCX ). The value of  sumsq  is
 assumed to be non-negative and  scl  returns the value

    scl = max( scale, abs( x( i ) ) ).

 scale and sumsq must be supplied in SCALE and SUMSQ and
 scl and smsq are overwritten on SCALE and SUMSQ respectively.

 The routine makes only one pass through the vector x.

Parameters:

N

          N is INTEGER
          The number of elements to be used from the vector X.

X

          X is DOUBLE PRECISION array, dimension (N)
          The vector for which a scaled sum of squares is computed.
             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 DOUBLE PRECISION
          On entry, the value  scale  in the equation above.
          On exit, SCALE is overwritten with  scl , the scaling factor
          for the sum of squares.

SUMSQ

          SUMSQ is DOUBLE PRECISION
          On entry, the value  sumsq  in the equation above.
          On exit, SUMSQ is overwritten with  smsq , the basic sum of
          squares from which  scl  has been factored out.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 104 of file dlassq.f.

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