uniform_sampling.py

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

import numpy as np

from caffe2.python import core, schema
from caffe2.python.layers.layers import LayerParameter, ModelLayer


class UniformSampling(ModelLayer):
    """
    Uniform sampling `num_samples - len(input_record)` unique elements from the
    range [0, num_elements). `samples` is the concatenation of input_record and
    the samples. input_record is expected to be unique.
    """

    def __init__(
        self,
        model,
        input_record,
        num_samples,
        num_elements,
        name='uniform_sampling',
        **kwargs
    ):
        super(UniformSampling, self).__init__(
            model, name, input_record, **kwargs
        )

        assert num_elements > 0
        assert isinstance(input_record, schema.Scalar)

        self.num_elements = num_elements

        self.num_samples = model.net.NextScopedBlob(name + "_num_samples")
        self.params.append(
            LayerParameter(
                parameter=self.num_samples,
                initializer=core.CreateOperator(
                    "GivenTensorInt64Fill",
                    [],
                    self.num_samples,
                    shape=(1, ),
                    values=[num_samples],
                ),
                optimizer=model.NoOptim,
            )
        )

        self.sampling_prob = model.net.NextScopedBlob(name + "_prob")
        self.params.append(
            LayerParameter(
                parameter=self.sampling_prob,
                initializer=core.CreateOperator(
                    "ConstantFill",
                    [],
                    self.sampling_prob,
                    shape=(num_samples, ),
                    value=float(num_samples) / num_elements,
                    dtype=core.DataType.FLOAT
                ),
                optimizer=model.NoOptim,
            )
        )

        self.output_schema = schema.Struct(
            (
                'samples', schema.Scalar(
                    np.int32, model.net.NextScopedBlob(name + "_samples")
                )
            ),
            ('sampling_prob', schema.Scalar(np.float32, self.sampling_prob)),
        )

    def add_ops(self, net):
        net.StopGradient(self.sampling_prob, self.sampling_prob)

        shape = net.Shape([self.input_record()], net.NextScopedBlob("shape"))
        shape = net.Sub([self.num_samples, shape], shape)
        samples = net.UniqueUniformFill(
            [shape, self.input_record()],
            net.NextScopedBlob("samples"),
            min=0,
            max=self.num_elements - 1,
            input_as_shape=True
        )

        net.Concat(
            [self.input_record(), samples],
            [self.output_schema.samples(), net.NextScopedBlob("split_info")],
            axis=0
        )
        net.StopGradient(
            self.output_schema.samples(), self.output_schema.samples()
        )