.. 
    Copyright 2020 The HuggingFace Team. All rights reserved.

    Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
    the License. You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
    an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
    specific language governing permissions and limitations under the License.

M2M100
-----------------------------------------------------------------------------------------------------------------------

Overview
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The M2M100 model was proposed in `Beyond English-Centric Multilingual Machine Translation
<https://arxiv.org/abs/2010.11125>`__ by Angela Fan, Shruti Bhosale, Holger Schwenk, Zhiyi Ma, Ahmed El-Kishky,
Siddharth Goyal, Mandeep Baines, Onur Celebi, Guillaume Wenzek, Vishrav Chaudhary, Naman Goyal, Tom Birch, Vitaliy
Liptchinsky, Sergey Edunov, Edouard Grave, Michael Auli, Armand Joulin.

The abstract from the paper is the following:

*Existing work in translation demonstrated the potential of massively multilingual machine translation by training a
single model able to translate between any pair of languages. However, much of this work is English-Centric by training
only on data which was translated from or to English. While this is supported by large sources of training data, it
does not reflect translation needs worldwide. In this work, we create a true Many-to-Many multilingual translation
model that can translate directly between any pair of 100 languages. We build and open source a training dataset that
covers thousands of language directions with supervised data, created through large-scale mining. Then, we explore how
to effectively increase model capacity through a combination of dense scaling and language-specific sparse parameters
to create high quality models. Our focus on non-English-Centric models brings gains of more than 10 BLEU when directly
translating between non-English directions while performing competitively to the best single systems of WMT. We
open-source our scripts so that others may reproduce the data, evaluation, and final M2M-100 model.*


Training and Generation
_______________________________________________________________________________________________________________________

M2M100 is a multilingual encoder-decoder (seq-to-seq) model primarily intended for translation tasks. As the model is
multilingual it expects the sequences in a certain format: A special language id token is used as prefix in both the
source and target text. The source text format is :obj:`[lang_code] X [eos]`, where :obj:`lang_code` is source language
id for source text and target language id for target text, with :obj:`X` being the source or target text.

- Supervised Training

.. code-block::

    from transformers import M2M100Config, M2M100ForConditionalGeneration, M2M100Tokenizer

    model = M2M100ForConditionalGeneration.from_pretrained('facebook/m2m100_418M')
    tokenizer = M2M100Tokenizer.from_pretrained('facebook/m2m100_418M', src_lang="en", tgt_lang="fr")

    src_text = "Life is like a box of chocolates."
    tgt_lang = "La vie est comme une boîte de chocolat."

    model_inputs = tokenizer(src_text, return_tensors="pt")
    with tokenizer.as_target_tokenizer():
        labels = tokenizer(tgt_text, return_tensors="pt").input_ids

    loss = model(**model_inputs, labels=labels) # forward pass


- Generation

    M2M100 uses the :obj:`eos_token_id` as the :obj:`decoder_start_token_id` for generation with the target language id
    being forced as the first generated token. To force the target language id as the first generated token, pass the
    `forced_bos_token_id` parameter to the `generate` method. The following example shows how to translate between
    Hindi to French and Chinese to English using the `facebook/m2m100_418M` checkpoint.

.. code-block::

    >>> from transformers import M2M100ForConditionalGeneration, M2M100Tokenizer

    >>> hi_text = "जीवन एक चॉकलेट बॉक्स की तरह है।"
    >>> chinese_text = "生活就像一盒巧克力。"

    >>> model = M2M100ForConditionalGeneration.from_pretrained("facebook/m2m100_418M")
    >>> tokenizer = M2M100Tokenizer.from_pretrained("facebook/m2m100_418M")

    >>> # translate Hindi to French
    >>> tokenizer.src_lang = "hi"
    >>> encoded_hi = tokenizer(hi_text, return_tensors="pt")
    >>> generated_tokens = model.generate(**encoded_hi, forced_bos_token_id=tokenizer.get_lang_id("fr"))
    >>> tokenizer.batch_decode(generated_tokens, skip_special_tokens=True)
    "La vie est comme une boîte de chocolat."

    >>> # translate Chinese to English
    >>> tokenizer.src_lang = "ar_AR"
    >>> encoded_zh = tokenizer(chinese_text, return_tensors="pt")
    >>> generated_tokens = model.generate(**encoded_zh, forced_bos_token_id=tokenizer.get_lang_id("en"))
    >>> tokenizer.batch_decode(generated_tokens, skip_special_tokens=True)
    "Life is like a box of chocolate."


M2M100Config
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. autoclass:: transformers.M2M100Config
    :members:


M2M100Tokenizer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. autoclass:: transformers.M2M100Tokenizer
    :members: build_inputs_with_special_tokens, get_special_tokens_mask,
        create_token_type_ids_from_sequences, save_vocabulary


M2M100Model
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. autoclass:: transformers.M2M100Model
    :members: forward


M2M100ForConditionalGeneration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. autoclass:: transformers.M2M100ForConditionalGeneration
    :members: forward


