Merge pull request #3327 from niboshi/doc-initializer

Document initializer criteria

chainer/links/connection/linear.py

@@ -24,14 +24,11 @@ class Linear(link.Link):
             data pass at which time the size will be determined.
         out_size (int): Dimension of output vectors.
         nobias (bool): If ``True``, then this function does not use the bias.
-        initialW (2-D array): Initial weight value. If ``None``, then the
-            default initializer is used.
-            May also be a callable that takes ``numpy.ndarray`` or
-            ``cupy.ndarray`` and edits its value.
-        initial_bias (1-D array): Initial bias value. If ``None``, the bias
-            vector is initialized to zero.
-            May also be a callable that takes ``numpy.ndarray`` or
-            ``cupy.ndarray`` and edits its value.
+        initialW (:ref:`initializer <initializer>`): Initializer to initialize
+            the weight.
+        initial_bias (:ref:`initializer <initializer>`): Initializer to
+            initialize the bias. If ``None``, the bias will be initialized to
+            zero.
     .. seealso:: :func:`~chainer.functions.linear`
 
     Attributes:

docs/source/reference/initializers.rst

@@ -1,10 +1,23 @@
+.. _initializer:
+
 Weight Initializers
 ===================
 
-Weight initializer is an instance of :class:`~chainer.Initializer` that
-destructively edits the contents of :class:`numpy.ndarray` or :class:`cupy.ndarray`.
-Typically, weight initializers are passed to ``__init__`` of :class:`~chainer.Link`
-and initializes its the weights and biases.
+Weight initializers are used to initialize arrays.
+They destructively modify the content of :class:`numpy.ndarray`
+or :class:`cupy.ndarray`.
+Typically, weight initializers are passed to :class:`~chainer.Link`\ s
+to initialize their weights and biases.
+
+A weight initializer can be any of the following objects.
+
+* :class:`chainer.Initializer` class instance.
+* Python or NumPy scalar.
+* A callable that takes an array (:class:`numpy.ndarray` or :class:`cupy.ndarray`)
+  and feeds the initial data into it.
+* ``None``, in which case *the default initializer* is used.
+  Unless explicitly specified, it is :class:`~chainer.initializers.LeCunNormal`
+  with scale value 1.
 
 Base class
 ----------