# Copyright (c) Microsoft Corporation.
# Licensed under the MIT license.
from typing import cast
import torch
import torch.nn as nn
import torch.nn.functional as F
class StackedLSTMCell(nn.Module):
def __init__(self, layers, size, bias):
super().__init__()
self.lstm_num_layers = layers
self.lstm_modules = nn.ModuleList([nn.LSTMCell(size, size, bias=bias)
for _ in range(self.lstm_num_layers)])
def forward(self, inputs, hidden):
prev_h, prev_c = hidden
next_h, next_c = [], []
for i, m in enumerate(self.lstm_modules):
curr_h, curr_c = m(inputs, (prev_h[i], prev_c[i]))
next_c.append(curr_c)
next_h.append(curr_h)
# current implementation only supports batch size equals 1,
# but the algorithm does not necessarily have this limitation
inputs = curr_h[-1].view(1, -1)
return next_h, next_c
class ReinforceField:
"""
A field with ``name``, with ``total`` choices. ``choose_one`` is true if one and only one is meant to be
selected. Otherwise, any number of choices can be chosen.
"""
def __init__(self, name, total, choose_one):
self.name = name
self.total = total
self.choose_one = choose_one
def __repr__(self):
return f'ReinforceField(name={self.name}, total={self.total}, choose_one={self.choose_one})'
[docs]class ReinforceController(nn.Module):
"""
A controller that mutates the graph with RL.
Parameters
----------
fields : list of ReinforceField
List of fields to choose.
lstm_size : int
Controller LSTM hidden units.
lstm_num_layers : int
Number of layers for stacked LSTM.
tanh_constant : float
Logits will be equal to ``tanh_constant * tanh(logits)``. Don't use ``tanh`` if this value is ``None``.
skip_target : float
Target probability that skipconnect (chosen by InputChoice) will appear.
If the chosen number of inputs is away from the ``skip_connect``, there will be
a sample skip penalty which is a KL divergence added.
temperature : float
Temperature constant that divides the logits.
entropy_reduction : str
Can be one of ``sum`` and ``mean``. How the entropy of multi-input-choice is reduced.
"""
def __init__(self, fields, lstm_size=64, lstm_num_layers=1, tanh_constant=1.5,
skip_target=0.4, temperature=None, entropy_reduction='sum'):
super(ReinforceController, self).__init__()
self.fields = fields
self.lstm_size = lstm_size
self.lstm_num_layers = lstm_num_layers
self.tanh_constant = tanh_constant
self.temperature = temperature
self.skip_target = skip_target
self.lstm = StackedLSTMCell(self.lstm_num_layers, self.lstm_size, False)
self.attn_anchor = nn.Linear(self.lstm_size, self.lstm_size, bias=False)
self.attn_query = nn.Linear(self.lstm_size, self.lstm_size, bias=False)
self.v_attn = nn.Linear(self.lstm_size, 1, bias=False)
self.g_emb = nn.Parameter(torch.randn(1, self.lstm_size) * 0.1)
self.skip_targets = nn.Parameter(torch.tensor([1.0 - self.skip_target, self.skip_target]), # pylint: disable=not-callable
requires_grad=False)
assert entropy_reduction in ['sum', 'mean'], 'Entropy reduction must be one of sum and mean.'
self.entropy_reduction = torch.sum if entropy_reduction == 'sum' else torch.mean
self.cross_entropy_loss = nn.CrossEntropyLoss(reduction='none')
self.soft = nn.ModuleDict({
field.name: nn.Linear(self.lstm_size, field.total, bias=False) for field in fields
})
self.embedding = nn.ModuleDict({
field.name: nn.Embedding(field.total, self.lstm_size) for field in fields
})
def resample(self, return_prob=False):
self._initialize()
result = dict()
for field in self.fields:
result[field.name] = self._sample_single(field, return_prob=return_prob)
return result
def _initialize(self):
self._inputs = self.g_emb.data
self._c = [torch.zeros((1, self.lstm_size),
dtype=self._inputs.dtype,
device=self._inputs.device) for _ in range(self.lstm_num_layers)]
self._h = [torch.zeros((1, self.lstm_size),
dtype=self._inputs.dtype,
device=self._inputs.device) for _ in range(self.lstm_num_layers)]
self.sample_log_prob: torch.Tensor = cast(torch.Tensor, 0)
self.sample_entropy: torch.Tensor = cast(torch.Tensor, 0)
self.sample_skip_penalty: torch.Tensor = cast(torch.Tensor, 0)
def _lstm_next_step(self):
self._h, self._c = self.lstm(self._inputs, (self._h, self._c))
def _sample_single(self, field, return_prob):
self._lstm_next_step()
logit = self.soft[field.name](self._h[-1])
if self.temperature is not None:
logit /= self.temperature
if self.tanh_constant is not None:
logit = self.tanh_constant * torch.tanh(logit)
if field.choose_one:
sampled_dist = F.softmax(logit, dim=-1)
sampled = torch.multinomial(F.softmax(logit, dim=-1), 1).view(-1)
log_prob = self.cross_entropy_loss(logit, sampled)
self._inputs = self.embedding[field.name](sampled)
else:
sampled_dist = torch.sigmoid(logit)
logit = logit.view(-1, 1)
logit = torch.cat([-logit, logit], 1) # pylint: disable=invalid-unary-operand-type
sampled = torch.multinomial(F.softmax(logit, dim=-1), 1).view(-1)
skip_prob = torch.sigmoid(logit)
kl = torch.sum(skip_prob * torch.log(skip_prob / self.skip_targets))
self.sample_skip_penalty += kl
log_prob = self.cross_entropy_loss(logit, sampled)
sampled = sampled.nonzero().view(-1)
if sampled.sum().item():
self._inputs = (torch.sum(self.embedding[field.name](sampled.view(-1)), 0) / (1. + torch.sum(sampled))).unsqueeze(0)
else:
self._inputs = torch.zeros(1, self.lstm_size, device=self.embedding[field.name].weight.device) # type: ignore
sampled = sampled.detach().cpu().numpy().tolist()
self.sample_log_prob += self.entropy_reduction(log_prob)
entropy = (log_prob * torch.exp(-log_prob)).detach() # pylint: disable=invalid-unary-operand-type
self.sample_entropy += self.entropy_reduction(entropy)
if len(sampled) == 1:
sampled = sampled[0]
if return_prob:
return sampled_dist.flatten().detach().cpu().numpy().tolist()
return sampled