This is the list of changes made after the release of Aspect version 2.1.0. All entries are signed with the names of the author.

1. New: There is a new material model that combines viscous, elastic and plastic deformation for one or more materials. At present, the model does not take into account diffusion or dislocation creep flow laws and strain softening.
   (John Naliboff, 2019/05/24)

2. New: This adds a new, alternative stabilization method for the advection called SUPG. This is preliminary work.
   (Rene Gassmoeller, Timo Heister, Ryan Grove, 2019/05/24)

3. Changed: The BoundaryVelocity::Manager::get_prescribed_boundary_velocity() function has been removed. It had previously already been removed.
   (Wolfgang Bangerth, 2019/05/22)

4. Changed: The BoundaryVelocity::Manager::get_active_boundary_velocity_conditions() function used to return a std::vector of std::shared_ptr objects to heating models enabled for the current run. This has been changed: It now returns a std::vector of std::unique_ptr objects.
   (Wolfgang Bangerth, 2019/05/22)

5. Changed: The InitialComposition::Manager::get_active_initial_composition_conditions() function used to return a std::vector of std::shared_ptr objects to heating models enabled for the current run. This has been changed: It now returns a std::vector of std::unique_ptr objects.
   (Wolfgang Bangerth, 2019/05/22)

6. Changed: The entropy viscosity method for stabilizing the advection equations for temperature and composition was substantially improved. A bugfix allowed to reduce the stabilization parameters to the old defaults that were published in the Kronbichler et al 2012 article. Additionally, boundary layers that are conduction dominated are not longer unnecessarily stabilized, which results in a more accurate heat flux, a better overall heat-flux balance, and closer agreement with existing benchmark cases. The old implementation was not wrong, but it required an unnecessarily high resolution to correctly resolve boundary layers. The 'artificial viscosity' postprocessor can always be used to check the amount of applied artificial diffusion.
   (Rene Gassmoeller, 2019/05/13)

7. Fixed: There was an interpolation bug in the 'gplates' boundary velocity plugin that lead to constant spherical velocities in a small spherical wedge right below the 0 meridian. The missing interpolation lead to a small velocity jump right at the 0 meridian. This is fixed now.
   (Rene Gassmoeller, 2019/05/08)

8. Changed: The lateral averaging functions, e.g. used in the 'depth average' postprocessor were optimized for some geometry models (spherical shell, box, two merged boxes). Their lateral averaging is now slightly less accurate (the difference is typically on the order of 1e-3 at the coarsest resolutions and disappears with higher refinement), but they will be around 5 (2D) to 25 (3D) times faster.
   (Rene Gassmoeller, 2019/05/05)

9. Changed: The BoundaryTemperature::Manager::get_active_boundary_temperature_conditions() function used to return a std::vector of std::shared_ptr objects. This has been changed: The function now returns a std::vector of std::unique_ptr objects.
   (Wolfgang Bangerth, 2019/05/02)

10. Changed: The HeatingModels::Manager::get_heating_models() function used to return a std::vector of std::shared_ptr objects to heating models enabled for the current run. This has been changed: It now returns a std::vector of std::unique_ptr objects.
    (Wolfgang Bangerth, 2019/05/02)

11. New: ASPECT now requires deal.II version 9.0.0 or newer.
    (Timo Heister and Rene Gassmoeller, 2019/04/25)

12. New: There is a new termination criterion that cancels the model run when a steady state average temperature is reached.
    (Rene Gassmoeller, Juliane Dannberg, Eva Bredow, 2019/01/09)

13. Incompatibility: When selecting the 'dynamic core' plugin for the boundary temperature, the plugin previously used the "Dynamic core" spelling with a leading upper-case letter. However, all other plugins use leading lower-case letters. Consequently, the plugin was changed to follow the usual convention using all lower-case letters, even though this is a change that requires changes to users' input files.
    (Wolfgang Bangerth, 2018/06/21)