import numpy
from chainer import cuda
from chainer import function
from chainer import utils
from chainer.utils import type_check
class Maximum(function.Function):
"""Element-wise maximum of input variables."""
def check_type_forward(self, in_types):
type_check.expect(
in_types.size() == 2,
in_types[0].dtype.kind == 'f',
in_types[0].dtype == in_types[1].dtype,
in_types[0].shape == in_types[1].shape
)
def forward_cpu(self, inputs):
x1, x2 = inputs
y = numpy.maximum(x1, x2)
return utils.force_array(y),
def backward_cpu(self, inputs, grads):
x1, x2 = inputs
gy, = grads
gx1 = gy * (x1 >= x2)
gx2 = gy * (x1 < x2)
return utils.force_array(gx1), utils.force_array(gx2)
def forward_gpu(self, inputs):
x1, x2 = inputs
return cuda.cupy.maximum(x1, x2),
def backward_gpu(self, inputs, grads):
x1, x2 = inputs
gy, = grads
gx1 = cuda.elementwise(
'T x1, T x2, T gy', 'T gx1',
'gx1 = (x1 >= x2) ? gy : (T)0.0',
'maximum_bwd1')(x1, x2, gy)
gx2 = cuda.elementwise(
'T x1, T x2, T gy', 'T gx1',
'gx1 = (x1 < x2) ? gy : (T)0.0',
'maximum_bwd2')(x1, x2, gy)
return gx1, gx2
[docs]def maximum(x1, x2):
"""Element-wise maximum of input variables.
Args:
x1 (~chainer.Variable): Input variables to be compared.
x2 (~chainer.Variable): Input variables to be compared.
Returns:
~chainer.Variable: Output variable.
"""
return Maximum()(x1, x2)