naginterfaces.library.blas.idrank

naginterfaces.library.blas.idrank(x, tol)

idrank determines the index of the first negligible element of a real vector.

For full information please refer to the NAG Library document for f06kl

https://www.nag.com/numeric/nl/nagdoc_29.3/flhtml/f06/f06klf.html

Parameters

xfloat, array-like, shape $\left(n\right)$

The $n$-element vector $x$.

tolfloat

The value $\text{tol}$.

Returns

kint

The index of the first negligible element of the real vector.

Raises

NagValueError

(errno $3$)

On entry, error in parameter $\text{incx}$.

Constraint: $\text{incx}>0$.

Notes

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

idrank finds the first element of the $n$-element real vector $x$ for which

$$\left|x_{k+1}\right|\le \text{tol}max(\left|x_1\right|,\dots ,\left|x_k\right|)$$

and returns the index $k$. If no such $k$ exists, then the value $n$ is returned. If a negative value of $\text{tol}$ is supplied, the value of machine precision is used in place of $\text{tol}$.