Fix/fixed point jacobi convergence

Issue/feature addressed

The intended idea in NekLinSysIterFixedpointJacobi.cpp seems to estimate the error norm by taking the difference between two successive iterations. For this purpose, the call to the Vmath::Vcopy should be done after the convergence check. Also, the SysResNorm variable in NekSys.cpp represents the L2 norm squared (L2norm^2), not the actual L2 norm.

Proposed solution

Implementation

Tests

Suggested reviewers

Please suggest any people who would be appropriate to review your code.

Notes

These two issues only affect LinSysIterDemo.cpp which is not critical to the core of the Nektar++ framework.

Checklist

• [ ] Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• [ ] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).