naginterfaces.library.blas.daxpyi

naginterfaces.library.blas.daxpyi(a, x, indx, y)

daxpyi adds a scaled sparse real vector, stored in compressed form, to an unscaled real vector.

For full information please refer to the NAG Library document for f06et

https://support.nag.com/numeric/nl/nagdoc_30.3/flhtml/f06/f06etf.html

Parameters

afloat

The scalar $\alpha$.

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

The nonzero elements of the sparse vector $x$.

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

$indx[\text{i}-1]$ must contain the index of $x[\text{i}-1]$ in the sparse vector $x$, for $\text{i}=1,2,\dots ,\text{nz}$.

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

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

Returns

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

The updated vector $y$.

Notes

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

daxpyi performs the operation

$$y\leftarrow \alpha x+y$$

where $x$ is a sparse real vector, stored in compressed form, and $y$ is a real vector in full storage form.

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