NAG CL Interface
f11xac (real_​gen_​matvec)

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

1: $\mathbf{trans}$ – Nag_TransType Input

On entry: specifies whether or not the matrix $A$ is transposed.

$\mathbf{trans}=\mathrm{Nag\_NoTrans}$

$y=Ax$ is computed.

$\mathbf{trans}=\mathrm{Nag\_Trans}$

$y=A^{\mathrm{T}}x$ is computed.

Constraint: $\mathbf{trans}=\mathrm{Nag\_NoTrans}$ or $\mathrm{Nag\_Trans}$.

2: $\mathbf{n}$ – Integer Input

On entry: $n$, the order of the matrix $A$.

Constraint: $\mathbf{n}\ge 1$.

3: $\mathbf{nnz}$ – Integer Input

On entry: the number of nonzero elements in the matrix $A$.

Constraint: $1\le \mathbf{nnz}\le {\mathbf{n}}^2$.

4: $\mathbf{a}\left[\mathbf{nnz}\right]$ – const double Input

On entry: the nonzero elements in the matrix $A$, ordered by increasing row index, and by increasing column index within each row. Multiple entries for the same row and column indices are not permitted. The function f11zac may be used to order the elements in this way.

5: $\mathbf{irow}\left[\mathbf{nnz}\right]$ – const Integer Input

6: $\mathbf{icol}\left[\mathbf{nnz}\right]$ – const Integer Input

On entry: the row and column indices of the nonzero elements supplied in array a.

Constraints:

irow and icol must satisfy the following constraints (which may be imposed by a call to f11zac):

• $1\le \mathbf{irow}\left[\mathit{i}\right]\le \mathbf{n}$ and $1\le \mathbf{icol}\left[\mathit{i}\right]\le \mathbf{n}$, for $\mathit{i}=0,1,\dots ,\mathbf{nnz}-1$;
• $\mathbf{irow}\left[\mathit{i}-1\right]<\mathbf{irow}\left[\mathit{i}\right]$ or $\mathbf{irow}\left[\mathit{i}-1\right]=\mathbf{irow}\left[\mathit{i}\right]$ and $\mathbf{icol}\left[\mathit{i}-1\right]<\mathbf{icol}\left[\mathit{i}\right]$, for $\mathit{i}=1,2,\dots ,\mathbf{nnz}-1$.

7: $\mathbf{check}$ – Nag_SparseNsym_CheckData Input

On entry: specifies whether or not the CS representation of the matrix $A$, values of n, nnz, irow and icol should be checked.

$\mathbf{check}=\mathrm{Nag\_SparseNsym\_Check}$

Checks are carried on the values of n, nnz, irow and icol.

$\mathbf{check}=\mathrm{Nag\_SparseNsym\_NoCheck}$

None of these checks are carried out.

See also Section 9.2.

Constraint: $\mathbf{check}=\mathrm{Nag\_SparseNsym\_Check}$ or $\mathrm{Nag\_SparseNsym\_NoCheck}$.

8: $\mathbf{x}\left[\mathbf{n}\right]$ – const double Input

On entry: the vector $x$.

9: $\mathbf{y}\left[\mathbf{n}\right]$ – double Output

On exit: the vector $y$.

10: $\mathbf{fail}$ – NagError * Input/Output

The NAG error argument (see Section 7 in the Introduction to the NAG Library CL Interface).

6 Error Indicators and Warnings

A nonzero element has been supplied which does not lie within the matrix $A$, is out of order, or has duplicate row and column indices. Consider calling f11zac to reorder and sum or remove duplicates.

NE_ALLOC_FAIL

Dynamic memory allocation failed.
See Section 3.1.2 in the Introduction to the NAG Library CL Interface for further information.

NE_BAD_PARAM

On entry, argument $〈\mathit{\text{value}}〉$ had an illegal value.

NE_INT

On entry, $\mathbf{n}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{n}\ge 1$.

On entry, $\mathbf{nnz}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{nnz}\ge 1$.

NE_INT_2

On entry, $\mathbf{nnz}=〈\mathit{\text{value}}〉$ and $\mathbf{n}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{nnz}\le {\mathbf{n}}^2$.

NE_INTERNAL_ERROR

An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
See Section 7.5 in the Introduction to the NAG Library CL Interface for further information.

NE_INVALID_CS

On entry, $i=〈\mathit{\text{value}}〉$, $\mathbf{icol}\left[i-1\right]=〈\mathit{\text{value}}〉$ and $\mathbf{n}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{icol}\left[i-1\right]\ge 1$ and $\mathbf{icol}\left[i-1\right]\le \mathbf{n}$.

On entry, $i=〈\mathit{\text{value}}〉$, $\mathbf{irow}\left[i-1\right]=〈\mathit{\text{value}}〉$ and $\mathbf{n}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{irow}\left[i-1\right]\ge 1$ and $\mathbf{irow}\left[i-1\right]\le \mathbf{n}$.

NE_NO_LICENCE

Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library CL Interface for further information.

NE_NOT_STRICTLY_INCREASING

On entry, $\mathbf{a}\left[i-1\right]$ is out of order: $i=〈\mathit{\text{value}}〉$.

On entry, the location ($\mathbf{irow}\left[\mathit{I}-1\right],\mathbf{icol}\left[\mathit{I}-1\right]$) is a duplicate: $\mathit{I}=〈\mathit{\text{value}}〉$.

7 Accuracy

8 Parallelism and Performance

9 Further Comments

9.1 Timing

9.2 Use of check

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results