Source code for quantum_launcher.problems.problem_formulations.bqm

 1from typing import Tuple
 2import ast
 3import numpy as np
 4from pyqubo import Spin
 5from quantum_launcher.base import adapter, formatter
 6from quantum_launcher.problems.problem_initialization import Raw
 7
 8

[docs]
 9@adapter('qubo', 'bqm')
10def qubo_to_bqm(qubo_with_offset) -> dict:
11    qubo, offset = qubo_with_offset
12    bqm, _ = QUBOMatrix(qubo, offset).qubo_matrix_into_bqm()
13    return bqm

14
15

[docs]
16class QUBOMatrix:
17    def __init__(self, qubo_matrix, offset):
18        self.qubo_matrix = qubo_matrix
19        self.offset = offset
20
21        if type(self.qubo_matrix) == str:
22            self.qubo_matrix = np.array(ast.literal_eval(self.qubo_matrix))
23
24        self.symetric = True
25        self._check_if_symetric()
26
27    def _check_if_symetric(self):
28        """
29        Function to check if matrix is symetric
30        """
31        self.symetric = (self.qubo_matrix.transpose()
32                         == self.qubo_matrix).all()
33        if not self.symetric:
34            self.qubo_matrix = self._remove_lower_triangle(self.qubo_matrix)
35
36    def _remove_lower_triangle(self, matrix):
37        """
38        Function to remove lower triangle from matrix
39        """
40        for i in range(len(matrix)):
41            for j in range(len(matrix)):
42                if i > j:
43                    matrix[i][j] = 0
44        return matrix
45
46    def _get_values_and_qubits(self, matrix):
47        """
48        Function to get values and qubits from matrix in form of dictionary
49        where keys are indexes of qubits and values are values of matrix
50        The function does not take into account zeros in matrix
51        Example:
52        matrix = [[0,1,2],[1,0,3],[2,3,0]]
53        result = {(0,1):1, (0,2):2, (1,0):1, (1,2):3, (2,0):2, (2,1):3}
54        Function also return second value which is the number of qubits
55        """
56        result = {
57            (x, y): c for y, r in enumerate(matrix) for x, c in enumerate(r) if c != 0
58        }
59        return result, len(matrix)
60

[docs]
61    def qubo_matrix_into_bqm(self):
62        values_and_qubits, number_of_qubits = self._get_values_and_qubits(
63            self.qubo_matrix
64        )
65        qubits = [Spin(f"x{i}") for i in range(number_of_qubits)]
66        H = 0
67        for (x, y), value in values_and_qubits.items():
68            if self.symetric:
69                H += value / len(set((x, y))) * qubits[x] * qubits[y]
70            else:
71                H += value * qubits[x] * qubits[y]
72        model = H.compile()
73        bqm = model.to_bqm()
74        bqm.offset += self.offset
75        return bqm, model


76
77

[docs]
78@formatter(Raw, 'bqm')
79def Rawbqm(problem: Raw):
80    return problem.instance