Changes since last release

Users: If you are working with the develop branch and your local code or project has been broken by a recent interface change then please see here for fix suggestions.

Developers: Please mention any changes to the code which will break users’ code here - to be put in the release notes for the next release. Also mention any significant improvements or new features. The real definitive release notes will be written in release notes at the time of release. To make that process easier, please structure this page in the same manner.

Changes since last release appear below

(changes since Release 2026.1)

Headline features

  • #513 The cell-based force hierarchy has been refactored, replacing GeneralisedLinearSpringForce and related classes with dedicated force classes. This is a breaking API change; see Cell Based below for the replacements.
  • #557 Chaste has adopted the Contributor Covenant code of conduct.

Dependency changes

This will be the last Chaste release to support Ubuntu 22.04 LTS (Jammy), and the following dependencies versions will no longer be supported in future releases.

  • Boost < 1.83
  • HDF5 < 1.10.10
  • PETSc < 3.19
  • SUNDIALS < 6.4
  • VTK < 9.1
  • GCC < 13
  • Clang < 18
  • CMake < 3.28

Newly supported dependency versions:

  • #521 HDF5 2.0 and 2.1 are now supported.
  • #522 PETSc 3.25 is now supported.
  • #526 XSD 4.2 is now supported.

Removed dependency versions:

  • #559 PyChaste now requires Python 3.10 or later. Python 3.9 is no longer supported.

Core

  • #548 Chaste now sets explicit permissions on the files and directories it creates rather than inheriting the platform default. This resolves some, but not all, of the sporadic permission-related test failures seen in the Docker container on macOS.
  • #562 gperftools CPU profiling is supported again: the CMake machinery has been restored and runs in CI, and can also be run locally by following the profiling guide.

Heart

Cell Based

  • #513 The cell-based force hierarchy has been refactored. GeneralisedLinearSpringForce, RepulsionForce and DifferentialAdhesionGeneralisedLinearSpringForce are removed in favour of dedicated classes that work across both mesh-based and node-based populations:
    • LinearSpringForce: Meineke-style linear springs;
    • PathmanathanInteractionForce: logarithmic repulsion / exponential attraction;
    • SimpleLogarithmicRepulsionForce: repulsion only;
    • DifferentialAdhesionLinearSpringForce / DifferentialAdhesionPathmanathanInteractionForce: differential-adhesion variants.
  • #511 Added RK4NumericalMethod, a 4th-order Runge-Kutta numerical method for off-lattice cell mechanics, as a drop-in alternative to ForwardEulerNumericalMethod. Also adds NoNumericalMethod, required for the cell populations that update node positions with their own machinery (NodeBasedCellPopulationWithBuskeUpdate and ImmersedBoundaryCellPopulation). Fixes a bug in the step-halving adaptive-timestep loop, which may change results for simulations using an adaptive timestep.

PyChaste

  • #588 PyChaste now builds against cppwg 0.5.0, which brings two user-facing improvements:
    • Templated methods accept a subscript form, so population.AddCellWriter["CellLabelWriter"]() may be written in place of population.AddCellWriterCellLabelWriter().
    • Every wrapped class is now reachable at the top level as chaste.Foo, in addition to chaste.<subpackage>.Foo.

Future Plans

Next
Release notes