naginterfaces.library.blas.dnorm

naginterfaces.library.blas.dnorm(scal, ssq)

dnorm completes the safe computation of the Euclidean length of a vector, following a call to dssq() or dzssq().

For full information please refer to the NAG Library document for f06bm

https://support.nag.com/numeric/nl/nagdoc_30.2/flhtml/f06/f06bmf.html

Parameters

scalfloat

The scaling factor $\alpha$, returned by dssq() or dzssq().

ssqfloat

The scaled sum of squares $\xi$, returned by dssq() or dzssq().

Returns

nrm2float

The Euclidean length of the vector.

Raises

NagValueError

(errno $1$)

On entry, error in parameter $scal$.

Constraint: $scal\ge 0.0$.

(errno $2$)

On entry, error in parameter $ssq$.

Constraint: $ssq\ge 1.0$.

Notes

No equivalent traditional C interface for this routine exists in the NAG Library.

dnorm completes the safe computation of the Euclidean length of a vector, following a call to dssq() or dzssq() which return values $\alpha$ and $\xi$ such that

$${\parallel x\parallel }_2^2={\alpha }^2\xi \text{.}$$

dnorm returns the value

$$min(\alpha \sqrt{\xi },\text{flmax})\text{,}$$

where $\text{flmax}$ is the value given by $1/\left(\text{machine.real\_safe}\right)$.