Class find_embedding::embedding¶

template<typename embedding_problem_t>
class embedding¶ This class is how we represent and manipulate embedding objects, using as much encapsulation as possible.
We provide methods to view and modify chains.
Public Functions

inline embedding(embedding_problem_t &e_p)¶
constructor for an empty embedding

inline embedding(embedding_problem_t &e_p, map<int, vector<int>> &fixed_chains, map<int, vector<int>> &initial_chains)¶
constructor for an initial embedding: accepts fixed and initial chains, populates the embedding based on them, and attempts to link adjacent chains together.

inline embedding<embedding_problem_t> &operator=(const embedding<embedding_problem_t> &other)¶
copy the data from
other.var_embedding
intothis.var_embedding

inline unsigned int chainsize(int v) const¶
Get the size of a chain.

inline int weight(int q) const¶
Get the weight of a qubit.

inline int max_weight() const¶
Get the maximum of all qubit weights.

inline int max_weight(const int start, const int stop) const¶
Get the maximum of all qubit weights in a range.

inline bool has_qubit(const int v, const int q) const¶
Check if variable v is includes qubit q in its chain.

inline void set_chain(const int u, const vector<int> &incoming)¶
Assign a chain for variable u.

inline void fix_chain(const int u, const vector<int> &incoming)¶
Permanently assign a chain for variable u.
NOTE: This must be done before any chain is assigned to u.

inline bool operator==(const embedding &other) const¶
check if
this
andother
have the same chains (up to qubit containment per chain; linking and parent information is not checked)

inline void construct_chain(const int u, const int q, const vector<vector<int>> &parents)¶
construct the chain for
u
, rooted atq
, with a vector of parent info, where for each neiborv
ofu
, followingq
>parents[v][q]
>parents[v][parents[v][q]]
…terminates in the chain for
v

inline void construct_chain_steiner(const int u, const int q, const vector<vector<int>> &parents, const vector<vector<distance_t>> &distances, vector<vector<int>> &visited_list)¶
construct the chain for
u
, rooted atq
.for the first neighbor
v
ofu
, we follow the parents until we terminate in the chain forv
q
>parents[v][q]
> …. adding all but the last node to the chain ofu
. for each subsequent neighborw
, we pick a nearest Steiner node,qw
, from the current chain ofu
, and add the path starting atqw
, similar to the above…qw
>parents[w][qw]
> … this has an opportunity to make shorter chains thanconstruct_chain

inline void flip_back(int u, const int target_chainsize)¶
distribute path segments to the neighboring chains — path segments are the qubits that are ONLY used to join link_qubit[u][v] to link_qubit[u][u] and aren’t used for any other variable
if the target chainsize is zero, dump the entire segment into the neighbor
if the target chainsize is k, stop when the neighbor’s size reaches k

inline void tear_out(int u)¶
short tearout procedure blank out the chain, its linking qubits, and account for the qubits being freed

inline int freeze_out(int u)¶
undoable tearout procedure.
similar to
tear_out(u)
, but can be undone withthaw_back(u)
. note that this embedding type has a space for a single frozen chain, andfreeze_out(u)
overwrites the previouslyfrozen chain consequently,freeze_out(u)
can be called an arbitrary (nonzero) number of times beforethaw_back(u)
, butthaw_back(u)
MUST be preceeded by at least onefreeze_out(u)
. returns the size of the chain being frozen

inline void thaw_back(int u)¶
undo for the freeze_out procedure: replaces the chain previously frozen, and destroys the data in the frozen chain
thaw_back(u)
must be preceeded by at least onefreeze_out(u)
and the chain foru
must currently be empty (accomplished either bytear_out(u)
orfreeze_out(u)
)

inline void steal_all(int u)¶
grow the chain for
u
, stealing all available qubits from neighboring variables

inline int statistics(vector<int> &stats) const¶
compute statistics for this embedding and return
1
if no chains are overlapping when no chains are overlapping, populatestats
with a chainlength histogram chains do overlap, populatestats
with a qubit overfill histogram a histogram, in this case, is a vector of size (maximum attained value+1) wherestats[i]
is either the number of qubits contained ini+2
chains or the number of chains with sizei

inline bool linked() const¶
check if the embedding is fully linked — that is, if each pair of adjacent variables is known to correspond to a pair of adjacent qubits

inline bool linked(int u) const¶
check if a single variable is linked with all adjacent variables.

inline void print() const¶
print out this embedding to a level of detail that is useful for debugging purposes TODO describe the output format.

inline void long_diagnostic(std::string current_state)¶
run a long diagnostic, and if debugging is enabled, record
current_state
so that the error message has a little more context.if an error is found, throw a CorruptEmbeddingException

inline void run_long_diagnostic(std::string current_state) const¶
run a long diagnostic to verify the integrity of this datastructure.
the guts of this function are its documentation, because this function only exists for debugging purposes

inline embedding(embedding_problem_t &e_p)¶