The following merged MRs are worth to be considered for mentioning in the changelog for 3.4. Please have a look and add their content in a few words if necessary, and then mark it in the checkbox. - [x] !2408 - [x] !2569 - [x] !2296 - [x] !2507 - [x] ~~!2285~~ (We want to include this new grid variable concept after this can be really used instead of still in namespace 'Experimental') - [x] !2521 - [x] !2510 - [x] !2509 - [x] !2505 - [x] !2243 - [x] !2239 The `LinearPDESolver` can reuse the matrix and thus avoid unnecessary reassembly. See `test/porousmediumflow/tracer/constvel/main.cc` for an example. - [x] !2414 - [x] !2454 - [x] !2421 - [x] !2457 - [x] !2422 - [x] !2419 : This MR is mentioned in the changelog for 3.3. Please check if this is correct. - [x] !2425 - [x] ~~!2282~~ (This was not merged into `master`but into the new staggered dev branch) - [x] !2417