remove "tridiag" from group "symmetric"

[KlausC]

Fix issue #121

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.15%. Comparing base (6412cec) to head (8c528a6). Report is 9 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #122 +/- ## ========================================== + Coverage 90.97% 93.15% +2.18% ========================================== Files 14 14 Lines 2437 2440 +3 ========================================== + Hits 2217 2273 +56 + Misses 220 167 -53 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.