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- """
- Provides an extremely basic graph structure, based on neighbour lists
- """
-
- from collections import defaultdict
- import itertools as it
- import clifford
-
-
- class GraphState(object):
-
- def __init__(self):
- self.ngbh = defaultdict(set)
- self.vops = defaultdict(int)
-
- def add_vertex(self, v):
- """ Add a vertex if it doesn't already exist """
- if not v in self.ngbh:
- self.ngbh[v] = set()
- self.vops[v] = clifford.by_name["hadamard"]
-
- def add_edge(self, v1, v2):
- """ Add an edge between two vertices in the self """
- if not v1 in self.ngbh:
- self.vops[v1] = clifford.by_name["hadamard"]
- if not v2 in self.ngbh:
- self.vops[v2] = clifford.by_name["hadamard"]
- self.ngbh[v1].add(v2)
- self.ngbh[v2].add(v1)
-
- def del_edge(self, v1, v2):
- """ Delete an edge between two vertices in the self """
- self.ngbh[v1].remove(v2)
- self.ngbh[v2].remove(v1)
-
- def has_edge(self, v1, v2):
- """ Test existence of an edge between two vertices in the self """
- return v2 in self.ngbh[v1]
-
- def toggle_edge(self, v1, v2):
- """ Toggle an edge between two vertices in the self """
- if self.has_edge(v1, v2):
- self.del_edge(v1, v2)
- else:
- self.add_edge(v1, v2)
-
- def edgelist(self):
- """ Describe a graph as an edgelist """
- edges = frozenset(tuple(sorted((i, n)))
- for i, v in self.ngbh.items()
- for n in v)
- return [tuple(e) for e in edges]
-
- def remove_vop(self, a, avoid):
- """ Reduces VOP[a] to the identity """
- others = self.ngbh[a] - {avoid}
- swap_qubit = others.pop() if others else avoid
- for v in reversed(clifford.decompositions[self.vops[a]]):
- self.local_complementation(a if v == "x" else swap_qubit)
-
- def local_complementation(self, v):
- """ As defined in LISTING 1 of Anders & Briegel """
- for i, j in it.combinations(self.ngbh[v], 2):
- self.toggle_edge(i, j)
-
- # Update VOPs: TODO check ordering and replace by self.act_local_rotation
- self.vops[v] = clifford.times_table[
- self.vops[v]][clifford.by_name["sqx"]]
- for i in self.ngbh[v]:
- self.vops[i] = clifford.times_table[
- self.vops[i]][clifford.by_name["msqz"]]
-
- def act_local_rotation(self, a, op):
- """ Act a local rotation """
- self.vops[a] = clifford.times_table[op,self.vops[a]]
-
- def act_cz(self, a, b):
- """ Act a controlled-phase gate on two qubits """
- if self.ngbh[a] - {b}:
- self.remove_vop(a, b)
- if self.ngbh[b] - {a}:
- self.remove_vop(b, a)
- if self.ngbh[a] - {b}:
- self.remove_vop(a, b)
- edge = self.has_edge(a, b)
- # TODO put this in a new function for diff hook
- new_edge, self.vops[a], self.vops[b] = clifford.cz_table[edge, self.vops[a], self.vops[b]]
- if new_edge != edge:
- self.toggle_edge(a, b)
-
- def __str__(self):
- """ Represent as a string for quick debugging """
- return "graph:\n vops: {}\n ngbh: {}\n"\
- .format(str(dict(self.vops)), str(dict(self.ngbh)))
-
-
- class DiffedGraphState(GraphState):
- """ Just like a graph state, but tracks changes for rendering purposes """
-
- def __init__(self):
- GraphState.__init__(self)
- self.diff = []
-
- def add_vertex(self, v):
- GraphState.add_vertex(self, v)
- self.diff.append("add_vertex {}".format(v))
-
- def add_edge(self, v1, v2):
- GraphState.add_edge(self, v1, v2)
- self.diff.append("add_edge {} {}".format(v1, v2))
-
-
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