Improves the bound estimation

Description

Improves the bound estimation

In particular this commit does the following:

• fixes a bug related to calling lalg_eigensolve after matrix_norm2. The tridiagonal matrix was destroyed and this was leading to a wrong lower bound. Fixing this seems to help a bit with the convergence.

• The calculation of the lower bound was a upper limit and not a lower limit. This is fixed by removing the norm of the residual.

• Tighter bounds are now obtained using the formula (2.6) in Y. Zhou, R.-C. Li / Linear Algebra and its Applications 435 (2011) 480–493

News snippet

Minor bugfix for the Chebyshev filtering.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

changed milestone to %14.0

added Bugfix Core labels

requested review from @AlexBuccheri

assigned to @nicolastd

added 1 commit

• ece9077f - Adjust reference values slightly.

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requested review from @heiko.appel

approved this merge request

As Heiko has already approved and the threads are minor, feel free to merge once the issue is added. Or ping me to have another look.

added 1 commit

• 66f95237 - Adjust reference values slightly.

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resolved all threads

enabled an automatic merge when the pipeline for 66f95237 succeeds

merged

mentioned in commit a7044ded

added in Changelog label