Embedding#

classtorch.nn.Embedding(num_embeddings,embedding_dim,padding_idx=None,max_norm=None,norm_type=2.0,scale_grad_by_freq=False,sparse=False,_weight=None,_freeze=False,device=None,dtype=None)[source]#

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 correspondingword embeddings.

Parameters

• num_embeddings (int) – size of the dictionary of embeddings

• embedding_dim (int) – the size of each embedding vector

• padding_idx (int,optional) – If specified, the entries atpadding_idx do not contribute to the gradient;therefore, the embedding vector atpadding_idx is not updated during training,i.e. it remains as a fixed “pad”. For a newly constructed Embedding,the embedding vector atpadding_idx will default to all zeros,but can be updated to another value to be used as the padding vector.

• max_norm (float,optional) – If given, each embedding vector with norm larger thanmax_normis renormalized to have normmax_norm.

• norm_type (float,optional) – The p of the p-norm to compute for themax_norm option. Default2.

• scale_grad_by_freq (bool,optional) – If given, this will scale gradients by the inverse of frequency ofthe words in the mini-batch. DefaultFalse.

• sparse (bool,optional) – IfTrue, gradient w.r.t.weight matrix will be a sparse tensor.See Notes for more details regarding sparse gradients.

Variables

weight (Tensor) – the learnable weights of the module of shape (num_embeddings, embedding_dim)initialized from$\mathcal{N}(0,1)$N(0,1)

Shape:

• Input:$(\ast )$(∗), IntTensor or LongTensor of arbitrary shape containing the indices to extract

• Output:$(\ast ,H)$(∗,H), where* is the input shape and$H=\text{embedding\_dim}$H=embedding_dim

Note

Keep in mind that only a limited number of optimizers supportsparse gradients: currently it’soptim.SGD (CUDA andCPU),optim.SparseAdam (CUDA andCPU) andoptim.Adagrad (CPU)

Note

Whenmax_norm is notNone,Embedding’s forward method will modify theweight tensor in-place. Since tensors needed for gradient computations cannot bemodified in-place, performing a differentiable operation onEmbedding.weight beforecallingEmbedding’s forward method requires cloningEmbedding.weight whenmax_norm is notNone. For example:

n,d,m=3,5,7embedding=nn.Embedding(n,d,max_norm=1.0)W=torch.randn((m,d),requires_grad=True)idx=torch.tensor([1,2])a=(embedding.weight.clone()@W.t())# weight must be cloned for this to be differentiableb=embedding(idx)@W.t()# modifies weight in-placeout=a.unsqueeze(0)+b.unsqueeze(1)loss=out.sigmoid().prod()loss.backward()

Examples:

>>># an Embedding module containing 10 tensors of size 3>>>embedding=nn.Embedding(10,3)>>># a batch of 2 samples of 4 indices each>>>input=torch.LongTensor([[1,2,4,5],[4,3,2,9]])>>>embedding(input)tensor([[[-0.0251, -1.6902,  0.7172],         [-0.6431,  0.0748,  0.6969],         [ 1.4970,  1.3448, -0.9685],         [-0.3677, -2.7265, -0.1685]],        [[ 1.4970,  1.3448, -0.9685],         [ 0.4362, -0.4004,  0.9400],         [-0.6431,  0.0748,  0.6969],         [ 0.9124, -2.3616,  1.1151]]])>>># example with padding_idx>>>embedding=nn.Embedding(10,3,padding_idx=0)>>>input=torch.LongTensor([[0,2,0,5]])>>>embedding(input)tensor([[[ 0.0000,  0.0000,  0.0000],         [ 0.1535, -2.0309,  0.9315],         [ 0.0000,  0.0000,  0.0000],         [-0.1655,  0.9897,  0.0635]]])>>># example of changing `pad` vector>>>padding_idx=0>>>embedding=nn.Embedding(3,3,padding_idx=padding_idx)>>>embedding.weightParameter containing:tensor([[ 0.0000,  0.0000,  0.0000],        [-0.7895, -0.7089, -0.0364],        [ 0.6778,  0.5803,  0.2678]], requires_grad=True)>>>withtorch.no_grad():...embedding.weight[padding_idx]=torch.ones(3)>>>embedding.weightParameter containing:tensor([[ 1.0000,  1.0000,  1.0000],        [-0.7895, -0.7089, -0.0364],        [ 0.6778,  0.5803,  0.2678]], requires_grad=True)

classmethodfrom_pretrained(embeddings,freeze=True,padding_idx=None,max_norm=None,norm_type=2.0,scale_grad_by_freq=False,sparse=False)[source]#

Create Embedding instance from given 2-dimensional FloatTensor.

Parameters

• embeddings (Tensor) – FloatTensor containing weights for the Embedding.First dimension is being passed to Embedding asnum_embeddings, second asembedding_dim.

• freeze (bool,optional) – IfTrue, the tensor does not get updated in the learning process.Equivalent toembedding.weight.requires_grad=False. Default:True

• padding_idx (int,optional) – If specified, the entries atpadding_idx do not contribute to the gradient;therefore, the embedding vector atpadding_idx is not updated during training,i.e. it remains as a fixed “pad”.

• max_norm (float,optional) – See module initialization documentation.

• norm_type (float,optional) – See module initialization documentation. Default2.

• scale_grad_by_freq (bool,optional) – See module initialization documentation. DefaultFalse.

• sparse (bool,optional) – See module initialization documentation.

Examples:

>>># FloatTensor containing pretrained weights>>>weight=torch.FloatTensor([[1,2.3,3],[4,5.1,6.3]])>>>embedding=nn.Embedding.from_pretrained(weight)>>># Get embeddings for index 1>>>input=torch.LongTensor([1])>>>embedding(input)tensor([[ 4.0000,  5.1000,  6.3000]])