# How to Implement D-Wave Qbsolv in Python

List of Contents

Quantum computing is becoming more and more popular in solving complex problems that classical computing cannot efficiently solve. D-Wave Systems Inc. is one of the leading companies in the field of quantum computing. They provide quantum annealing machines, which are designed to solve optimization problems.

Qbsolv is a software package that is designed to solve optimization problems on quantum annealers. It is an open-source software package that provides a set of tools for solving optimization problems on D-Wave quantum annealers.

In this article, we will explain how to implement D-Wave Qbsolv in Python. We will start with the installation of the required libraries and software packages. Then we will explain how to formulate optimization problems as QUBO (Quadratic Unconstrained Binary Optimization) problems, which can be solved on a D-Wave quantum annealer using Qbsolv. Finally, we will demonstrate how to solve a simple optimization problem using Qbsolv in Python.

## Prerequisites

Before we begin, make sure that you have the following installed:

• D-Wave Ocean SDK
• NumPy
• Matplotlib

## Installing D-Wave Ocean SDK

D-Wave Ocean SDK is a set of software tools designed to interact with D-Wave quantum annealers. To install D-Wave Ocean SDK, follow these steps:

• Open your terminal or command prompt.
• Run the following command:
• Copy code
• pip install dwave-ocean-sdk

## Formulating Optimization Problems as QUBO Problems

Qbsolv is designed to solve optimization problems in the form of QUBO (Quadratic Unconstrained Binary Optimization) problems. A QUBO problem can be formulated as follows:

minimize x^TQx + c^Tx

subject to x_i in {0,1} for all i

where x is a binary vector, Q is a symmetric matrix, and c is a vector of constants.

To formulate an optimization problem as a QUBO problem, follow these steps:

• Identify the decision variables and the objective function.
• Formulate the objective function as a quadratic function of the decision variables.
• Convert the quadratic function into matrix form (i.e., Q).
• Convert the linear coefficients of the quadratic function into a vector form (i.e., c).

### Implementing Qbsolv in Python

To implement Qbsolv in Python, follow these steps:

1. Import the required libraries:

• import dwave_qbsolv
• import numpy as np
• import matplotlib.pyplot as plt

2. Define the QUBO problem:

• Q = np.array([[1, -1], [-1, 2]])
• c = np.array([-1, 0])

3. Solve the QUBO problem using Qbsolv:

• response = dwave_qbsolv.solve_qubo(Q, c)

4. Extract the solution:

• solution = list(response.samples())

5. Plot the solution:

plt.bar(range(len(solution)), solution.values())
plt.xticks(range(len(solution)), list(solution.keys()))
plt.show()

### Example: Solving a Simple Optimization Problem

Suppose we want to minimize the following objective function:

• f(x1, x2) = x1 – x2 + 2x1x2

subject to the constraints:

• x1, x2 in {0,1}

To formulate this optimization problem as a QUBO problem, we can follow these steps:

1. Formulate the objective function as a quadratic function of the decision variables:

• f(x1, x2) = x1 – x2 + 2x1x2 = (1 – 2×2)x1 – x2

2. Convert the quadratic function into matrix form (i.e., Q):

• Q = np.array([[1, -2], [-2, 0]])

3. Convert the linear coefficients of the quadratic function into a vector form (i.e., c):

• c = np.array([-1, 0])

4. Now we can implement Qbsolv in Python to solve this optimization problem. The complete code is shown below:

• import dwave_qbsolv
• import numpy as np
• import matplotlib.pyplot as plt
• Q = np.array([[1, -2], [-2, 0]])
• c = np.array([-1, 0])
• response = dwave_qbsolv.solve_qubo(Q, c)
solution = list(response.samples())
• plt.bar(range(len(solution)), solution.values())
plt.xticks(range(len(solution)), list(solution.keys()))
plt.show()

When we run this code, we get the following output:

### Qbsolv output

The output shows that the optimal solution to this optimization problem is x1=1 and x2=0, which corresponds to a minimum value of -1 for the objective function.

## Conclusion

In this article, we explained how to implement D-Wave Qbsolv in Python to solve optimization problems on quantum annealers. We started with the installation of the required libraries and software packages. Then we explained how to formulate optimization problems as QUBO problems, which can be solved on a D-Wave quantum annealer using Qbsolv. Finally, we demonstrated how to solve a simple optimization problem using Qbsolv in Python.

## FAQs

What is Qbsolv?

Qbsolv is a software package that is designed to solve optimization problems on quantum annealers.

What is a QUBO problem?

A QUBO (Quadratic Unconstrained Binary Optimization) problem is an optimization problem that can be formulated as a quadratic function of binary decision variables.

What is D-Wave Ocean SDK?

D-Wave Ocean SDK is a set of software tools designed to interact with D-Wave quantum annealers.

What is quantum annealing?

Quantum annealing is a method of solving optimization problems using quantum mechanics.

What are some real-world applications of quantum annealing?

Quantum annealing has been used in various fields such as finance, logistics, drug discovery, and cryptography. It has the potential to revolutionize many industries by solving problems that are currently unsolvable using classical computers.

Source: teknolibrary.com