Bug? nn.Parameter doesn't work with sparse input

1

I have a very small network like this:

import torch.nn as nn

class ConEcNet(nn.Module):

    def __init__(self, input_dim, embedding_dim):
        super(ConEcNet, self).__init__()
        self.W_inputs = nn.Parameter(0.1*torch.randn(input_dim))
        self.W_0 = nn.Linear(input_dim, embedding_dim)

    def forward(self, inputs):
        return self.W_0(inputs * self.W_inputs)

i.e. the input vector is first multiplied elementwise by the vector in W_inputs (i.e. each input feature has an individual importance weight) and then passed to the linear layer W_0. This works fine if my inputs are a regular tensor, however, if the inputs are a sparse tensor, the first multiplication (inputs * self.W_inputs) results in a RuntimeError: mul operands have incompatible sizes.

Since I’m working with BOW features, I would really like to use sparse inputs. Does nn.Parameter in general not work with sparse tensors? Is there a way around this besides casting the inputs to a regular tensor?

I’m using torch version 1.5.0.

Example:

import numpy as np
from scipy.sparse import coo_matrix
import torch

def coo2tensor(coo):
    """
    convert scipy sparse coo matrix to sparse torch tensor
    """
    values = coo.data
    indices = np.vstack((coo.row, coo.col))
    i = torch.LongTensor(indices)
    v = torch.FloatTensor(values)
    shape = coo.shape
    return torch.sparse.FloatTensor(i, v, torch.Size(shape))

cnet = ConEcNet(10, 5)
a = torch.randn(3, 10)
cnet(a)  # works
b = coo2tensor(coo_matrix(np.random.randn(3, 10)))
cnet(c)  # runtime error
cnet.W_0(c)  # works