naginterfaces.library.blas.dgthrz

naginterfaces.library.blas.dgthrz(y, indx)

dgthrz gathers specified (usually nonzero) elements of a real vector $y$ in full storage form into a sparse real vector $x$ in compressed form. The specified elements of $y$ are set to zero.

For full information please refer to the NAG Library document for f06ev

https://support.nag.com/numeric/nl/nagdoc_30/flhtml/f06/f06evf.html

Parameters

yfloat, array-like, shape $(max\left(indx\right))$

The vector $y$. Only elements corresponding to indices in $indx$ are accessed.

indxint, array-like, shape $\left(\text{nz}\right)$

$indx[\text{i}-1]$ must contain the index $y[\text{i}-1]$, for $\text{i}=1,2,\dots ,\text{nz}$, which is to be gathered into $x$.

Returns

yfloat, ndarray, shape $(max\left(indx\right))$

The elements of $y$ corresponding to indices in $indx$ are set to zero.

xfloat, ndarray, shape $\left(\text{nz}\right)$

The compressed vector $x$.

Raises

NagValueError

(errno $4$)

On entry, error in parameter $indx$.

Constraint: the indices must be distinct.

Notes

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

dgthrz gathers the specified elements of a vector, $y$, in full storage form, into the equivalent sparse vector compressed form. The gathered elements of $y$ are set to zero.

References

Dodson, D S, Grimes, R G and Lewis, J G, 1991, Sparse extensions to the Fortran basic linear algebra subprograms, ACM Trans. Math. Software (17), 253–263