This is a list of changes introduced in each release that users should be aware of when migrating from older versions. Most changes are carefully designed not to break existing code; however changes that may possibly break them are highlighted with a box.

## Chainer v3¶

### Introduction of New-style Functions¶

This release introduces new-style functions (classes inheriting from FunctionNode) that support double backward (gradient of gradient). See the Release Note for v3.0.0 for the usage of this feature.

Many of Standard Function implementations are already migrated to new-style, although some of functions are still old-style (classes inheriting from Function). We are going to migrate more old-style functions to new-style in upcoming minor releases.

This does not break the existing code. Old-style functions (classes inheriting from Function) are still supported in v3 and future versions of Chainer.

If you are going to write new functions, it is encouraged to use FunctionNode to support double backward.

Attention

Users relying on undocumented function APIs (directly instantiating old-style classes) may experience an error like TypeError: 'SomeFunction' object is not callable after upgrading to v3. Please use the function APIs documented in Standard Function implementations.

### Changed Behavior of matmul Function¶

The behavior of chainer.functions.matmul() has been changed to behave like the corresponding NumPy function (numpy.matmul()). See the discussion in #2426 for more details.

Attention

The existing code using chainer.functions.matmul() may require modification to work with Chainer v3.

Also note that chainer.functions.batch_matmul() is now deprecated by this change. You can rewrite it using chainer.functions.matmul().

### Removed use_cudnn Argument in spatial_transformer_grid and spatial_transformer_sampler Functions¶

use_cudnn argument has been removed from chainer.functions.spatial_transformer_grid() and chainer.functions.spatial_transformer_sampler(). See the discussion in #2955 for more details.

Attention

The existing code using use_cudnn argument of chainer.functions.spatial_transformer_grid() and chainer.functions.spatial_transformer_sampler() require modification to work with Chainer v3. Please use the configuration context (e.g., with chainer.using_config('use_cudnn', 'auto'):) to enable or disable use of cuDNN. See Configuring Chainer for details.

## Chainer v2¶

See Upgrade Guide from v1 to v2 for the changes introduced in Chainer v2.