Source code for gpytorch.variational.lmc_variational_strategy

#!/usr/bin/env python3

import torch

from ..distributions import MultitaskMultivariateNormal
from ..lazy import KroneckerProductLazyTensor, MatmulLazyTensor
from ..module import Module
from ._variational_strategy import _VariationalStrategy

[docs]class LMCVariationalStrategy(_VariationalStrategy): r""" LMCVariationalStrategy is an implementation of the "Linear Model of Coregionalization" for multitask GPs. This model assumes that there are :math:`Q` latent functions :math:`\mathbf g(\cdot) = [g^{(1)}(\cdot), \ldots, g^{(q)}(\cdot)]`, each of which is modelled by a GP. The output functions (tasks) are linear combination of the latent functions: .. math:: f_{\text{task } i}( \mathbf x) = \sum_{q=1}^Q a_i^{(q)} g^{(q)} ( \mathbf x ) LMCVariationalStrategy wraps an existing :obj:`~gpytorch.variational.VariationalStrategy` to produce a :obj:`~gpytorch.variational.MultitaskMultivariateNormal` distribution. The base variational strategy is assumed to operate on a multi-batch of GPs, where one of the batch dimensions corresponds to the latent function dimension. .. note:: The batch shape of the base :obj:`~gpytorch.variational.VariationalStrategy` does not necessarily have to correspond to the batch shape of the underlying GP objects. For example, if the base variational strategy has a batch shape of `[3]` (corresponding to 3 latent functions), the GP kernel object could have a batch shape of `[3]` or no batch shape. This would correspond to each of the latent functions having different kernels or the same kernel, respectivly. :param ~gpytorch.variational.VariationalStrategy base_variational_strategy: Base variational strategy :param int num_tasks: The total number of tasks (output functions) :param int num_latents: The total number of latent functions in each group :param latent_dim: (Default: -1) Which batch dimension corresponds to the latent function batch. **Must be negative indexed** :type latent_dim: `int` < 0 Example: >>> class LMCMultitaskGP(gpytorch.models.ApproximateGP): >>> ''' >>> 3 latent functions >>> 5 output dimensions (tasks) >>> ''' >>> def __init__(self): >>> # Each latent function shares the same inducing points >>> # We'll have 32 inducing points, and let's assume the input dimensionality is 2 >>> inducing_points = torch.randn(32, 2) >>> >>> # The variational parameters have a batch_shape of [3] - for 3 latent functions >>> variational_distribution = gpytorch.variational.MeanFieldVariationalDistribution( >>> inducing_points.size(-1), batch_shape=torch.Size([3]), >>> ) >>> variational_strategy = gpytorch.variational.LMCVariationalStrategy( >>> gpytorch.variational.VariationalStrategy( >>> inducing_points, variational_distribution, learn_inducing_locations=True, >>> ), >>> num_tasks=5, >>> num_latents=3, >>> latent_dim=0, >>> ) >>> >>> # Each latent function has its own mean/kernel function >>> super().__init__(variational_strategy) >>> self.mean_module = gpytorch.means.ConstantMean(batch_shape=torch.Size([3])) >>> self.covar_module = gpytorch.kernels.ScaleKernel( >>> gpytorch.kernels.RBFKernel(batch_shape=torch.Size([3])), >>> batch_shape=torch.Size([3]), >>> ) >>> >>> # Model output: n x 5 """ def __init__( self, base_variational_strategy, num_tasks, num_latents=1, latent_dim=0, ): Module.__init__(self) self.base_variational_strategy = base_variational_strategy self.num_tasks = num_tasks batch_shape = self.base_variational_strategy._variational_distribution.batch_shape # Check if no functions if latent_dim >= 0: raise RuntimeError(f"latent_dim must be a negative indexed batch dimension: got {latent_dim}.") if not (batch_shape[latent_dim] == num_latents or batch_shape[latent_dim] == 1): raise RuntimeError( f"Mismatch in num_latents: got a variational distribution of batch shape {batch_shape}, " f"expected the function dim {latent_dim} to be {num_latents}." ) self.num_latents = num_latents self.latent_dim = latent_dim # Make the batch_shape self.batch_shape = list(batch_shape) del self.batch_shape[self.latent_dim] self.batch_shape = torch.Size(self.batch_shape) # LCM coefficients lmc_coefficients = torch.randn(*batch_shape, self.num_tasks) self.register_parameter("lmc_coefficients", torch.nn.Parameter(lmc_coefficients)) @property def prior_distribution(self): return self.base_variational_strategy.prior_distribution @property def variational_distribution(self): return self.base_variational_strategy.variational_distribution @property def variational_params_initialized(self): return self.base_variational_strategy.variational_params_initialized def kl_divergence(self): return super().kl_divergence().sum(dim=self.latent_dim) def __call__(self, x, prior=False): function_dist = self.base_variational_strategy(x, prior=prior) lmc_coefficients = self.lmc_coefficients.expand(*function_dist.batch_shape, self.lmc_coefficients.size(-1)) num_batch = len(function_dist.batch_shape) num_dim = num_batch + len(function_dist.event_shape) latent_dim = num_batch + self.latent_dim if self.latent_dim is not None else None # Mean mean = function_dist.mean.permute(*range(0, latent_dim), *range(latent_dim + 1, num_dim), latent_dim) mean = mean @ lmc_coefficients.permute( *range(0, latent_dim), *range(latent_dim + 1, num_dim - 1), latent_dim, -1 ) # Covar covar = function_dist.lazy_covariance_matrix lmc_factor = MatmulLazyTensor(lmc_coefficients.unsqueeze(-1), lmc_coefficients.unsqueeze(-2)) covar = KroneckerProductLazyTensor(covar, lmc_factor) covar = covar.sum(latent_dim) # Add a bit of jitter to make the covar PD covar = covar.add_jitter(1e-6) # Done! function_dist = MultitaskMultivariateNormal(mean, covar) return function_dist