from chainer import cuda
from chainer import function
from chainer import utils
from chainer.utils import type_check
class Sqrt(function.Function):
@property
def label(self):
return 'sqrt'
def check_type_forward(self, in_types):
type_check.expect(
in_types.size() == 1,
in_types[0].dtype.kind == 'f',
)
def forward(self, x):
xp = cuda.get_array_module(*x)
return utils.force_array(xp.sqrt(x[0], dtype=x[0].dtype)),
def backward(self, x, gy):
xp = cuda.get_array_module(*x)
gx = utils.force_array(xp.sqrt(x[0], dtype=x[0].dtype))
gx *= 2.0
xp.reciprocal(gx, out=gx)
gx *= gy[0]
return gx,
[docs]def sqrt(x):
"""Elementwise square root function.
.. math::
y_i = \\sqrt x_i.
If the value of :math:`x_i` is negative, it returns ``Nan`` for :math:`y_i`
respect to underlying numpy and cupy specification.
Args:
x (~chainer.Variable): Input variable.
Returns:
~chainer.Variable: Output variable.
"""
return Sqrt()(x)
[docs]def rsqrt(x):
"""Computes elementwise reciprocal of square root of input :math:`x_i`.
.. math::
y_i = {1 \\over \\sqrt x_i}.
Args:
x (~chainer.Variable): Input variable.
Returns:
~chainer.Variable: Output variable.
.. seealso:: :func:`~chainer.functions.sqrt`
"""
return 1.0 / sqrt(x)