dlassq.f

Section: LAPACK (3)
Updated: Tue Nov 14 2017
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dlassq.f

SYNOPSIS

Functions/Subroutines

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

Function/Subroutine Documentation

subroutine dlassq (integer N, double precision, dimension( * ) X, integer INCX, double precision SCALE, double precision SUMSQ)

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