Contribution Guide has been updated! Please read it again!
We apologize that we could not fulfill the compatibility policy
in v2.0.0 (in particular, some changes are made without
explicit deprecation steps).
We have also updated the compatibility policy.
Important changes that affect user code
• CuPy is separated into a distinct repository/package
• Thread-local configuration chainer.config is introduced
• Training mode: chainer.config.train
• “volatile” is replaced by chainer.config.enable_backprop
• Interfaces of some links are changed
• Many deprecated classes/methods/functions are removed
Installation tips for GPU users
CuPy is now a separate package.
• If you have an old chainer, uninstall it first to clear CuPy:
pip uninstall chainer (repeat it until an error occurs)
• Then, install CuPy & Chainer by pip install cupy chainer
• If you are working with sudo, be careful that the environment
variables are not passed by default through sudo. If the nvcc
command is not found through PATH variable, cupy setup script fails.
New features (selected)
Aggressive buffer release
• Functions that do not require some of inputs for backprop
can release the array grabbed by the input nodes
• E.g.: F.relu and `+` can release the inputs
• It required refactoring of object relationships around
Variable and Function (so we introduced VariableNode)
New features (selected)
Fine-grained optimization control
• Optimizer.setup sets up update_rule to each parameter
• Each update rule can have its own hyperparameter
(e.g. learning rate)
• Each update rule can have its own hook function
(e.g. weight decay)
• Each update rule can be disabled (layer freezing)
New features (also included in v1)
• Variable and cupy.ndarray support advanced indexing
• Advanced indexing: indexing by integer index arrays and
Boolean mask arrays
• Variable’s advanced indexing also supports backprop
The main repository is moved to
Old path (pfnet/chainer) is automatically redirected to new
one (both on web and on git)
Related packages will also be developed under
New release cycle
No minor, 3 pre-releases, each release taking 4 weeks.
Versioned branches keep compatibility.
(v2, v3, v4, …)
• Differentiable backprop (a.k.a. backprop of backprop, double
backprop, higher order differentiation, etc.)
• Make a new-style Function whose backward() is implemented on
Function interface instead of ndarray
• Some more refactoring of object relationships around Variable
could be needed
• Documentation improvements, refactoring of tests
• Graph visualization toolkit?
• and more…
Discussions on the development
The main channel of the core dev team has moved to the
Chainer Slack team (request an invitation at bit.ly/chainer-slack)
• #develop for Chainer
• #develop-cupy for CuPy
These channels are public, so anyone can watch what is
going on in our daily development. Discussions on the
development are also welcome!