NAME

DLASSQ - return the values scl and smsq such that   ( scl∗∗2 )∗smsq = x( 1 )∗∗2 +...+ x( n )∗∗2 + ( scale∗∗2 )∗sumsq,

SYNOPSIS

SUBROUTINE DLASSQ(
N, X, INCX, SCALE, SUMSQ )

INTEGER INCX, N

DOUBLE PRECISION SCALE, SUMSQ

DOUBLE PRECISION X( ∗ )

PURPOSE

DLASSQ  returns the values  scl  and  smsq  such that
 
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.
 

ARGUMENTS

N       (input) INTEGER
The number of elements to be used from the vector X.

X       (input) DOUBLE PRECISION
The vector for which a scaled sum of squares is computed. x( i )  = X( 1 + ( i - 1 )∗INCX ), 1 <= i <= n.

INCX    (input) INTEGER
The increment between successive values of the vector X. INCX > 0.

SCALE   (input/output) 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   (input/output) 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.

  —  LAPACK version 2.0  —  08 October 1994