NAG CL Interface
f12acc (real_​proc)

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

1: $\mathbf{nconv}$ – Integer * Output

On exit: the number of converged eigenvalues as found by f12abc.

2: $\mathbf{dr}\left[\mathit{dim}\right]$ – double Output

Note: the dimension, dim, of the array dr must be at least $\mathbf{nev}+1$ (see f12aac).

On exit: the first nconv locations of the array dr contain the real parts of the converged approximate eigenvalues.

3: $\mathbf{di}\left[\mathit{dim}\right]$ – double Output

Note: the dimension, dim, of the array di must be at least $\mathbf{nev}+1$ (see f12aac).

On exit: the first nconv locations of the array di contain the imaginary parts of the converged approximate eigenvalues.

4: $\mathbf{z}\left[\mathbf{n}\times (\mathbf{nev}+1)\right]$ – double Output

On exit: if the default option $\mathbf{Vectors}=\mathrm{RITZ}$ (see f12adc) has been selected then z contains the final set of eigenvectors corresponding to the eigenvalues held in dr and di. The complex eigenvector associated with the eigenvalue with positive imaginary part is stored in two consecutive array segments. The first segment holds the real part of the eigenvector and the second holds the imaginary part. The eigenvector associated with the eigenvalue with negative imaginary part is simply the complex conjugate of the eigenvector associated with the positive imaginary part.

For example, the first eigenvector has real parts stored in locations $\mathbf{z}\left[\mathit{i}-1\right]$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$ and imaginary parts stored in $\mathbf{z}\left[\mathit{i}-1\right]$, for $\mathit{i}=\mathbf{n}+1,2\mathbf{n}$.

5: $\mathbf{sigmar}$ – double Input

On entry: if one of the $\mathbf{Shifted\; Inverse\; Real}$ modes have been selected then sigmar contains the real part of the shift used; otherwise sigmar is not referenced.

6: $\mathbf{sigmai}$ – double Input

On entry: if one of the $\mathbf{Shifted\; Inverse\; Real}$ modes have been selected then sigmai contains the imaginary part of the shift used; otherwise sigmai is not referenced.

7: $\mathbf{resid}\left[\mathit{dim}\right]$ – const double Input

Note: the dimension, dim, of the array resid must be at least $\mathbf{n}$ (see f12aac).

On entry: must not be modified following a call to f12abc since it contains data required by f12acc.

8: $\mathbf{v}\left[\mathbf{n}\times \mathbf{ncv}\right]$ – double Input/Output

The $\mathit{i}$th element of the $\mathit{j}$th basis vector is stored in location $\mathbf{v}\left[\mathbf{n}\times \left(\mathit{j}-1\right)+\mathit{i}-1\right]$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$ and $\mathit{j}=1,2,\dots ,\mathbf{ncv}$.

On entry: the ncv sections of v, of length $n$, contain the Arnoldi basis vectors for $\mathrm{op}$ as constructed by f12abc.

On exit: if the option $\mathbf{Vectors}=\mathrm{SCHUR}$ has been set, or the option $\mathbf{Vectors}=\mathrm{RITZ}$ has been set and a separate array z has been passed (i.e., z does not equal v), then the first nconv sections of v, of length $n$, will contain approximate Schur vectors that span the desired invariant subspace.

9: $\mathbf{comm}\left[\mathit{dim}\right]$ – double Communication Array

Note: the actual argument supplied must be the array comm supplied to the initialization routine f12aac.

On initial entry: must remain unchanged from the prior call to f12abc.

On exit: contains data on the current state of the solution.

10: $\mathbf{icomm}\left[\mathit{dim}\right]$ – Integer Communication Array

Note: the actual argument supplied must be the array icomm supplied to the initialization routine f12aac.

On initial entry: must remain unchanged from the prior call to f12abc.

On exit: contains data on the current state of the solution.

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

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

6 Error Indicators and Warnings

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_INITIALIZATION

Either the solver function has not been called prior to the call of this function or a communication array has become corrupted.

NE_INTERNAL_EIGVEC_FAIL

In calculating eigenvectors, an internal call returned with an error. Please contact NAG.

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_OPTION

On entry, $\mathbf{Vectors}=\mathrm{SELECT}$, but this is not yet implemented.

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_RITZ_COUNT

Got a different count of the number of converged Ritz values than the value passed to it through the argument icomm: number counted $=⟨\mathit{\text{value}}⟩$, number expected $=⟨\mathit{\text{value}}⟩$. This usually indicates that a communication array has been altered or has become corrupted between calls to f12abc and f12acc.

NE_SCHUR_EIG_FAIL

During calculation of a real Schur form, there was a failure to compute $⟨\mathit{\text{value}}⟩$ eigenvalues in a total of $⟨\mathit{\text{value}}⟩$ iterations.

NE_SCHUR_REORDER

The computed Schur form could not be reordered by an internal call. This function returned with $\mathbf{fail}\mathbf{.}\mathbf{code}=⟨\mathit{\text{value}}⟩$. Please contact NAG.

NE_ZERO_EIGS_FOUND

The number of eigenvalues found to sufficient accuracy, as communicated through the argument icomm, is zero. You should experiment with different values of nev and ncv, or select a different computational mode or increase the maximum number of iterations prior to calling f12abc.

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results