transformers/docs/source/en/model_doc/funnel.md

Funnel Transformer

Overview

The Funnel Transformer model was proposed in the paper Funnel-Transformer: Filtering out Sequential Redundancy for Efficient Language Processing. It is a bidirectional transformer model, like BERT, but with a pooling operation after each block of layers, a bit like in traditional convolutional neural networks (CNN) in computer vision.

The abstract from the paper is the following:

With the success of language pretraining, it is highly desirable to develop more efficient architectures of good scalability that can exploit the abundant unlabeled data at a lower cost. To improve the efficiency, we examine the much-overlooked redundancy in maintaining a full-length token-level presentation, especially for tasks that only require a single-vector presentation of the sequence. With this intuition, we propose Funnel-Transformer which gradually compresses the sequence of hidden states to a shorter one and hence reduces the computation cost. More importantly, by re-investing the saved FLOPs from length reduction in constructing a deeper or wider model, we further improve the model capacity. In addition, to perform token-level predictions as required by common pretraining objectives, Funnel-Transformer is able to recover a deep representation for each token from the reduced hidden sequence via a decoder. Empirically, with comparable or fewer FLOPs, Funnel-Transformer outperforms the standard Transformer on a wide variety of sequence-level prediction tasks, including text classification, language understanding, and reading comprehension.

This model was contributed by sgugger. The original code can be found here.

Usage tips

• Since Funnel Transformer uses pooling, the sequence length of the hidden states changes after each block of layers. This way, their length is divided by 2, which speeds up the computation of the next hidden states. The base model therefore has a final sequence length that is a quarter of the original one. This model can be used directly for tasks that just require a sentence summary (like sequence classification or multiple choice). For other tasks, the full model is used; this full model has a decoder that upsamples the final hidden states to the same sequence length as the input.
• For tasks such as classification, this is not a problem, but for tasks like masked language modeling or token classification, we need a hidden state with the same sequence length as the original input. In those cases, the final hidden states are upsampled to the input sequence length and go through two additional layers. That's why there are two versions of each checkpoint. The version suffixed with “-base” contains only the three blocks, while the version without that suffix contains the three blocks and the upsampling head with its additional layers.
• The Funnel Transformer checkpoints are all available with a full version and a base version. The first ones should be used for [FunnelModel], [FunnelForPreTraining], [FunnelForMaskedLM], [FunnelForTokenClassification] and [FunnelForQuestionAnswering]. The second ones should be used for [FunnelBaseModel], [FunnelForSequenceClassification] and [FunnelForMultipleChoice].

Resources

• Text classification task guide
• Token classification task guide
• Question answering task guide
• Masked language modeling task guide
• Multiple choice task guide

FunnelConfig

autodoc FunnelConfig

FunnelTokenizer

autodoc FunnelTokenizer - build_inputs_with_special_tokens - get_special_tokens_mask - create_token_type_ids_from_sequences - save_vocabulary

FunnelTokenizerFast

autodoc FunnelTokenizerFast

Funnel specific outputs

autodoc models.funnel.modeling_funnel.FunnelForPreTrainingOutput

autodoc models.funnel.modeling_tf_funnel.TFFunnelForPreTrainingOutput

FunnelBaseModel

autodoc FunnelBaseModel - forward

FunnelModel

autodoc FunnelModel - forward

FunnelModelForPreTraining

autodoc FunnelForPreTraining - forward

FunnelForMaskedLM

autodoc FunnelForMaskedLM - forward

FunnelForSequenceClassification

autodoc FunnelForSequenceClassification - forward

FunnelForMultipleChoice

autodoc FunnelForMultipleChoice - forward

FunnelForTokenClassification

autodoc FunnelForTokenClassification - forward

FunnelForQuestionAnswering

autodoc FunnelForQuestionAnswering - forward

TFFunnelBaseModel

autodoc TFFunnelBaseModel - call

TFFunnelModel

autodoc TFFunnelModel - call

TFFunnelModelForPreTraining

autodoc TFFunnelForPreTraining - call

TFFunnelForMaskedLM

autodoc TFFunnelForMaskedLM - call

TFFunnelForSequenceClassification

autodoc TFFunnelForSequenceClassification - call

TFFunnelForMultipleChoice

autodoc TFFunnelForMultipleChoice - call

TFFunnelForTokenClassification

autodoc TFFunnelForTokenClassification - call

TFFunnelForQuestionAnswering

autodoc TFFunnelForQuestionAnswering - call