/
prod.py
109 lines (87 loc) · 3.32 KB
/
prod.py
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import numpy
import six
from chainer import cuda
from chainer import function
from chainer.utils import type_check
class Prod(function.Function):
"""Product of array elements over a given axis."""
keepdims = False
def __init__(self, axis=None, keepdims=False):
if axis is None:
self.axis = None
elif isinstance(axis, int):
self.axis = (axis,)
elif isinstance(axis, tuple) and all(isinstance(a, int) for a in axis):
if len(set(axis)) != len(axis):
raise ValueError('duplicate value in axis: ({})'.format(
', '.join(map(str, axis))))
self.axis = axis
else:
raise TypeError('None, int or tuple of int are required')
self.keepdims = keepdims
def check_type_forward(self, in_types):
type_check.expect(
in_types.size() == 1,
in_types[0].dtype.kind == 'f',
)
if self.axis is not None:
for axis in self.axis:
if axis >= 0:
type_check.expect(
axis < in_types[0].ndim,
)
else:
type_check.expect(
-axis - 1 < in_types[0].ndim,
)
def forward(self, x):
xp = cuda.get_array_module(*x)
return xp.asarray(x[0].prod(axis=self.axis, keepdims=self.keepdims)),
def backward(self, x, gy):
xp = cuda.get_array_module(*x)
x = x[0]
gy = gy[0]
if self.axis is None:
axes = list(six.moves.range(x.ndim))
else:
axes = []
for axis in self.axis:
if axis < 0:
axis += len(x.shape)
axes.append(axis)
if not self.keepdims:
for axis in sorted(axes):
gy = xp.expand_dims(gy, axis=axis)
axes = tuple(axes)
# indices of axes that are not reduced
axes_kept = tuple(a for a in six.moves.range(x.ndim) if a not in axes)
n_reduced_elements = 1
for axis in axes:
n_reduced_elements *= x.shape[axis]
n_output_elements = x.size // n_reduced_elements
transpose_axes = axes_kept + axes
x = x.transpose(transpose_axes)
transposed_shape = x.shape
x = x.reshape(-1, n_reduced_elements)
extended_x = xp.repeat(x, n_reduced_elements, 0)
mask = xp.tile(xp.arange(n_reduced_elements), n_output_elements)
extended_x[xp.arange(x.size), mask] = 1
gx = extended_x.prod(1)
gx = gx.reshape(transposed_shape)
gx = gx.transpose(numpy.argsort(transpose_axes))
gx = gx * gy
return gx,
def prod(x, axis=None, keepdims=False):
"""Product of array elements over a given axis.
Args:
x (:class:`~chainer.Variable` or :class:`numpy.ndarray` or \
:class:`cupy.ndarray`): Elements to calculate the product.
axis (None, int, or tuple of int): Axis which a product is performed.
The default (axis = None) is perform a product over all the
dimensions of the input array.
keepdims (bool): If ``True``, the specified axes are remained as axes
of length one.
Returns:
~chainer.Variable: Output variable.
"""
return Prod(axis, keepdims)(x)