def subtensor(x, *ilists):
if idx_list:
cdata = get_idx_list((x,) + ilists, idx_list)
else:
cdata = ilists
if len(cdata) == 1:
cdata = cdata[0]
return x.__getitem__(cdata)
def local_subtensor_rv_lift(fgraph, node):
"""Lift ``*Subtensor`` `Op`s up to a `RandomVariable`'s parameters.
In a fashion similar to `local_dimshuffle_rv_lift`, the indexed dimensions
need to be separated into distinct replication-space and (independent)
parameter-space ``*Subtensor``s.
The replication-space ``*Subtensor`` can be used to determine a
sub/super-set of the replication-space and, thus, a "smaller"/"larger"
``size`` tuple. The parameter-space ``*Subtensor`` is simply lifted and
applied to the `RandomVariable`'s distribution parameters.
Consider the following example graph:
``normal(mu, std, size=(d1, d2, d3))[idx1, idx2, idx3]``. The
``*Subtensor`` `Op` requests indices ``idx1``, ``idx2``, and ``idx3``,
which correspond to all three ``size`` dimensions. Now, depending on the
broadcasted dimensions of ``mu`` and ``std``, this ``*Subtensor`` `Op`
could be reducing the ``size`` parameter and/or subsetting the independent
``mu`` and ``std`` parameters. Only once the dimensions are properly
separated into the two replication/parameter subspaces can we determine how
the ``*Subtensor`` indices are distributed.
For instance, ``normal(mu, std, size=(d1, d2, d3))[idx1, idx2, idx3]``
could become ``normal(mu[idx1], std[idx2], size=np.shape(idx1) + np.shape(idx2) + np.shape(idx3))``
if ``mu.shape == std.shape == ()``
``normal`` is a rather simple case, because it's univariate. Multivariate
cases require a mapping between the parameter space and the image of the
random variable. This may not always be possible, but for many common
distributions it is. For example, the dimensions of the multivariate
normal's image can be mapped directly to each dimension of its parameters.
We use these mappings to change a graph like ``multivariate_normal(mu, Sigma)[idx1]``
into ``multivariate_normal(mu[idx1], Sigma[idx1, idx1])``. Notice how
Also, there's the important matter of "advanced" indexing, which may not
only subset an array, but also broadcast it to a larger size.
"""
st_op = node.op
if not isinstance(st_op, (AdvancedSubtensor, AdvancedSubtensor1, Subtensor)):
return False
base_rv = node.inputs[0]
rv_node = base_rv.owner
if not (rv_node and isinstance(rv_node.op, RandomVariable)):
return False
# If no one else is using the underlying `RandomVariable`, then we can
# do this; otherwise, the graph would be internally inconsistent.
if not all(
(n == node or isinstance(n.op, Shape)) for n, i in fgraph.clients[base_rv]
):
return False
rv_op = rv_node.op
rng, size, dtype, *dist_params = rv_node.inputs
# TODO: Remove this once the multi-dimensional changes described below are
# in place.
if rv_op.ndim_supp > 0:
return False
rv_op = base_rv.owner.op
rng, size, dtype, *dist_params = base_rv.owner.inputs
idx_list = getattr(st_op, "idx_list", None)
if idx_list:
cdata = get_idx_list(node.inputs, idx_list)
else:
cdata = node.inputs[1:]
st_indices, st_is_bool = zip(
*tuple(
(as_index_variable(i), getattr(i, "dtype", None) == "bool") for i in cdata
)
)
# We need to separate dimensions into replications and independents
num_ind_dims = None
if len(dist_params) == 1:
num_ind_dims = dist_params[0].ndim
else:
# When there is more than one distribution parameter, assume that all
# of them will broadcast to the maximum number of dimensions
num_ind_dims = max(d.ndim for d in dist_params)
reps_ind_split_idx = base_rv.ndim - (num_ind_dims + rv_op.ndim_supp)
if len(st_indices) > reps_ind_split_idx:
# These are the indices that need to be applied to the parameters
ind_indices = tuple(st_indices[reps_ind_split_idx:])
# We need to broadcast the parameters before applying the `*Subtensor*`
# with these indices, because the indices could be referencing broadcast
# dimensions that don't exist (yet)
bcast_dist_params = broadcast_params(dist_params, rv_op.ndims_params)
# TODO: For multidimensional distributions, we need a map that tells us
# which dimensions of the parameters need to be indexed.
#
# For example, `multivariate_normal` would have the following:
# `RandomVariable.param_to_image_dims = ((0,), (0, 1))`
#
# I.e. the first parameter's (i.e. mean's) first dimension maps directly to
# the dimension of the RV's image, and its second parameter's
# (i.e. covariance's) first and second dimensions map directly to the
# dimension of the RV's image.
args_lifted = tuple(p[ind_indices] for p in bcast_dist_params)
else:
# In this case, no indexing is applied to the parameters; only the
# `size` parameter is affected.
args_lifted = dist_params
# TODO: Could use `ShapeFeature` info. We would need to be sure that
# `node` isn't in the results, though.
# if hasattr(fgraph, "shape_feature"):
# output_shape = fgraph.shape_feature.shape_of(node.outputs[0])
# else:
output_shape = indexed_result_shape(base_rv.shape, st_indices)
size_lifted = (
output_shape if rv_op.ndim_supp == 0 else output_shape[: -rv_op.ndim_supp]
)
# Boolean indices can actually change the `size` value (compared to just
# *which* dimensions of `size` are used).
if any(st_is_bool):
size_lifted = tuple(
tt_sum(idx) if is_bool else s
for s, is_bool, idx in zip(
size_lifted, st_is_bool, st_indices[: (reps_ind_split_idx + 1)]
)
)
new_node = rv_op.make_node(rng, size_lifted, dtype, *args_lifted)
_, new_rv = new_node.outputs
# Calling `Op.make_node` directly circumvents test value computations, so
# we need to compute the test values manually
if config.compute_test_value != "off":
compute_test_value(new_node)
return [new_rv]