Operator graph optimization tools¶
These functions are used to restructure the operator graph so that it can be simulated more efficiently when converted into a TensorFlow graph.

nengo_dl.graph_optimizer.
mergeable
(op, chosen_ops)[source]¶ Check if the given op can be merged with the candidate group
Parameters: Returns:  bool
True if
op
can be merged intochosen_ops
, else False

nengo_dl.graph_optimizer.
greedy_planner
(operators)[source]¶ Combine mergeable operators into groups that will be executed as a single computation.
Parameters:  operators : list of
Operator
all the
nengo
operators in a model (unordered)
Returns:  list of tuple of :class:`~nengo:nengo.builder.Operator`
operators combined into mergeable groups and in execution order
Notes
Originally based on
nengo_ocl
greedy planner operators : list of

nengo_dl.graph_optimizer.
tree_planner
(op_list, max_depth=3)[source]¶ Create merged execution plan through exhaustive tree search.
The
max_depth
parameter scales the planner between full tree search and greedy search.max_depth==1
is equivalent togreedy_planner()
, andmax_depth==len(op_list)
is full tree search (guaranteed to find the optimal plan, but likely very slow).Parameters:  op_list : list of
Operator
all the
nengo
operators in a model (unordered) max_depth : int, optional
the planner will search this many steps ahead before selecting which group to schedule next
Returns:  list of tuple of :class:`~nengo:nengo.builder.Operator`
operators combined into mergeable groups and in execution order
 op_list : list of

nengo_dl.graph_optimizer.
noop_planner
(operators)[source]¶ Orders operators into a valid execution order, but does not perform any merging.
Parameters:  operators : list of
Operator
all the
nengo
operators in a model (unordered)
Returns:  list of tuple of :class:`~nengo:nengo.builder.Operator`
operators in execution order
 operators : list of

nengo_dl.graph_optimizer.
transitive_planner
(op_list)[source]¶ Create merged execution plan through transitive closure construction.
This is something like a middle ground between
greedy_planner()
andtree_planner()
; it can improve simulation time over the greedy planner, but comes with potentially significant build time increases.Parameters:  op_list : list of
Operator
all the
nengo
operators in a model (unordered)
Returns:  list of tuple of :class:`~nengo:nengo.builder.Operator`
operators combined into mergeable groups and in execution order
 op_list : list of

nengo_dl.graph_optimizer.
transitive_closure_recurse
(dg, ops, trans, builder_type, builder_types, cache)[source]¶ Computes the transitive closure for the given graph, restricted to the operators with the given builder type.
Parameters:  dg : dict of {int: set of int}
dependency graph where
dg[a] = {b, c}
indicates that operatorsb
andc
are dependent ona
 ops : list of int
the operators for which we want to compute the transitive closure
 trans : dict of {int: set of int}
the transitive closure for the graph (will be filled inplace)
 builder_type : type
one of the
nengo_dl
build classes (e.g.,CopyBuilder
), specifying the type of operators to include in the transitive closure builder_types : list of type
the build class for each operator
 cache : dict of {frozenset of int: set of int}
stores base sets which
trans
will reference (to reduce memory usage, since many elements intrans
will have the same value)
Notes
This function uses ints to refer to operators, where the int indicates the index of the operator in the overall op list (this is done to save memory). See
transitive_planner()
.

nengo_dl.graph_optimizer.
order_signals
(plan, n_passes=10)[source]¶ Orders signals and operators to try to structure reads in contiguous blocks.
Parameters:  plan : list of tuple of
Operator
operator execution plan (e.g., output from
greedy_planner
) n_passes : int, optional
number of repeated passes through the operator reordering stage
Returns:  list of :class:`~nengo:nengo.builder.Signal`
signals organized into the order in which we want them arranged in memory
 list of tuple of :class:`~nengo:nengo.builder.Operator`
input plan with operators reordered within groups to align with order of signals
 plan : list of tuple of

nengo_dl.graph_optimizer.
hamming_sort
(blocks)[source]¶ Reorder signals using heuristics to try to place signals that are read by the same operators into adjacent positions (giving priority to larger blocks).
Parameters:  blocks : dict of {
Signal
: frozenset of int} dictionary indicating which read blocks each signal is a part of
Returns:  dict of {:class:`~nengo:nengo.builder.Signal`: int}
indices indicating where each signal should be in the sorted list
 blocks : dict of {

nengo_dl.graph_optimizer.
sort_ops_by_signals
(sorted_reads, sigs, sig_idxs, new_plan, blocks, reads)[source]¶ Rearrange operators to match the order of signals.
Note: the same operators can be associated with multiple read blocks if they have multiple inputs, so rearranging the operators according to one of those blocks could mess up the order with respect to the other read block. We iterate through the read blocks in increasing size so that the largest blocks win out.
Parameters:  sorted_reads : list of tuple of (
Operator
, int) the operators that form each read block, sorted by increasing size of the read block. in the case that a group of operators participate in multiple read blocks, the integer distinguishes which one of those inputs this block is associated with.
 sigs : list of
Signal
signals that have been arranged into a given order by other parts of the algorithm
 sig_idxs : dict of {
Signal
: int} sorted indices of signals
 new_plan : dict of {tuple of
Operator
: tuple ofOperator
} mapping from original operator group to the sorted operators
 blocks : dict of {
Signal
: frozenset of int} indicates which read blocks each signal participates in
 reads : dict of {
Operator
: list ofSignal
} the signals read by each operator
Returns:  sorted_reads : list of tuple of (

nengo_dl.graph_optimizer.
sort_signals_by_ops
(sorted_reads, sigs, sig_idxs, new_plan, blocks, reads)[source]¶ Attempts to rearrange
sigs
so that it is in the same order as operator reads, without changing the overall block order.Parameters:  sorted_reads : list of tuple of (
Operator
, int) the operators that form each read block, sorted by increasing size of the read block. in the case that a group of operators participate in multiple read blocks, the integer distinguishes which one of those inputs this block is associated with.
 sigs : list of
Signal
signals to be sorted
 sig_idxs : dict of {
Signal
: int} sorted indices of signals
 new_plan : dict of {tuple of
Operator
: tuple ofOperator
} mapping from original operator group to the sorted operators
 blocks : dict of {
Signal
: frozenset of int} indicates which read blocks each signal participates in
 reads : dict of {
Operator
: list ofSignal
} the signals read by each operator
Returns:  sig_idxs : dict of {
Signal
: int} sorted indices of signals
 sorted_reads : list of tuple of (

nengo_dl.graph_optimizer.
noop_order_signals
(plan, **kwargs)[source]¶ A version of
graph_optimizer.order_signals()
that doesn’t do any reordering, for debugging.

nengo_dl.graph_optimizer.
create_signals
(sigs, plan, float_type, minibatch_size)[source]¶ Groups signal data together into larger arrays, and represent each individual signal as a slice into that array.
Parameters:  sigs : list of
Signal
base signals arranged into the order in which they should reside in memory (e.g., output from
order_signals
) plan : list of tuple of
Operator
operator execution plan (only used to get a list of all the operators)
 float_type :
np.float32
ornp.float64
floating point precision to use for signals
 minibatch_size : int
number of items in each minibatch
Returns:  base_arrays : dict of {object
combined arrays, containing the initial values for all signals
 sig_map : dict of {
Signal
:signals.TensorSignal
} mapping from
nengo
Signals tonengo_dl
TensorSignals (views into the base arrays)
 sigs : list of

nengo_dl.graph_optimizer.
remove_unmodified_resets
(operators)[source]¶ Remove any Reset operators that are targeting a signal that is never modified.
If a signal is reset, but never inced/updated after that, we can just set the default signal value to the reset value and remove the reset. Note: this wouldn’t normally happen, but it can happen if we removed some of the incs (e.g. in remove_zero_incs).
Parameters:  operators : list of
Operator
operators in the model
Returns:  list of :class:`~nengo:nengo.builder.Operator`
modified list of operators
 operators : list of

nengo_dl.graph_optimizer.
remove_zero_incs
(operators)[source]¶ Remove any operators where we know the input (and therefore output) is zero.
If the input to a DotInc/ElementwiseInc/Copy is zero then we know that the output of the op will be zero, so we can just get rid of it.
Parameters:  operators : list of
Operator
operators in the model
Returns:  list of :class:`~nengo:nengo.builder.Operator`
modified list of operators
 operators : list of

nengo_dl.graph_optimizer.
remove_constant_copies
(operators)[source]¶ Change Copies with constant input to Resets.
If a Copy has no dependencies, or just one Reset() dependency, then we can change it to an op that just directly sets the output signal to the Copy input value.
Parameters:  operators : list of
Operator
operators in the model
Returns:  list of :class:`~nengo:nengo.builder.Operator`
modified list of operators
 operators : list of

nengo_dl.graph_optimizer.
remove_identity_muls
(operators)[source]¶ Change y=x*1 ops to y=x Copy ops.
If one of the inputs to a DotInc/ElementwiseInc is 1 then we can skip the multiplication and change it to a Copy op.
Parameters:  operators : list of
Operator
operators in the model
Returns:  list of :class:`~nengo:nengo.builder.Operator`
modified list of operators
 operators : list of