MegEngine/imperative/python/megengine/module/embedding.py

# -*- coding: utf-8 -*-
# MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
#
# Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
from typing import Optional

import numpy as np

from ..functional.nn import embedding as embedding_func
from ..tensor import Parameter
from . import init
from .module import Module


class Embedding(Module):
    r"""
    A simple lookup table that stores embeddings of a fixed dictionary and size.

    This module is often used to store word embeddings and retrieve them using indices.
    The input to the module is a list of indices, and the output is the corresponding word embeddings.
    The indices should less than num_embeddings.

    :param num_embeddings: size of embedding dictionary.
    :param embedding_dim: size of each embedding vector.
    :param padding_idx: should be set to None, not supportted now.
    :param max_norm: should be set to None, not supportted now.
    :param norm_type: should be set to None, not supportted now.
    :param initial_weight: the learnable weights of the module of shape (num_embeddings, embedding_dim).

    Examples:

    .. testcode::

        import numpy as np
        import megengine as mge
        import megengine.module as M
        weight = mge.tensor(np.array([(1.2,2.3,3.4,4.5,5.6)], dtype=np.float32))
        data = mge.tensor(np.array([(0,0)], dtype=np.int32))

        embedding = M.Embedding(1, 5, initial_weight=weight)
        output = embedding(data)
        with np.printoptions(precision=6):
            print(output.numpy())

    Outputs:

    .. testoutput::

        [[[1.2 2.3 3.4 4.5 5.6]
          [1.2 2.3 3.4 4.5 5.6]]]

    """

    def __init__(
        self,
        num_embeddings: int,
        embedding_dim: int,
        padding_idx: Optional[int] = None,
        max_norm: Optional[float] = None,
        norm_type: Optional[float] = None,
        initial_weight: Parameter = None,
        freeze: bool = False,
    ):
        super().__init__()
        if padding_idx is not None:
            raise ValueError("Not support padding index now.")
        if max_norm is not None or norm_type is not None:
            raise ValueError("Not support weight normalize now.")
        self.padding_idx = padding_idx
        self.max_norm = max_norm
        self.norm_type = norm_type
        self.num_embeddings = num_embeddings
        self.embedding_dim = embedding_dim
        self.freeze = freeze
        if initial_weight is None:
            self.weight = Parameter(
                np.random.uniform(
                    size=(self.num_embeddings, self.embedding_dim)
                ).astype(np.float32)
            )
            self.reset_parameters()
        else:
            if initial_weight.numpy().shape != (num_embeddings, embedding_dim):
                raise ValueError(
                    "The weight shape should match num_embeddings and embedding_dim"
                )
            self.weight = Parameter(initial_weight.numpy())

    def reset_parameters(self) -> None:
        init.normal_(self.weight)

    def forward(self, inputs):
        if self.freeze:
            weight = self.weight.detach()
        else:
            weight = self.weight
        return embedding_func(inputs, weight)

    @classmethod
    def from_pretrained(
        cls,
        embeddings: Parameter,
        freeze: Optional[bool] = True,
        padding_idx: Optional[int] = None,
        max_norm: Optional[float] = None,
        norm_type: Optional[float] = None,
    ):
        r"""
        Creates Embedding instance from given 2-dimensional FloatTensor.

        :param embeddings: tensor contained weight for the embedding.
        :param freeze: if ``True``, the weight does not get updated during the learning process. Default: True.
        :param padding_idx: should be set to None, not support Now.
        :param max_norm: should be set to None, not support Now.
        :param norm_type: should be set to None, not support Now.

        Examples:

        .. testcode::

            import numpy as np
            import megengine as mge
            import megengine.module as M
            weight = mge.tensor(np.array([(1.2,2.3,3.4,4.5,5.6)], dtype=np.float32))
            data = mge.tensor(np.array([(0,0)], dtype=np.int32))

            embedding = M.Embedding.from_pretrained(weight, freeze=False)
            output = embedding(data)
            print(output.numpy())

        Outputs:

        .. testoutput::

            [[[1.2 2.3 3.4 4.5 5.6]
              [1.2 2.3 3.4 4.5 5.6]]]

        """
        embeddings_shape = embeddings.shape
        embeddings_dim = len(embeddings_shape)
        if embeddings_dim != 2:
            raise ValueError("Embeddings parameter is expected to be 2-dimensional")
        rows = embeddings_shape[0]
        cols = embeddings_shape[1]
        embedding = cls(
            num_embeddings=rows,
            embedding_dim=cols,
            initial_weight=embeddings,
            padding_idx=padding_idx,
            max_norm=max_norm,
            norm_type=norm_type,
            freeze=freeze,
        )
        return embedding