QUBO stands for quadratic unconstrained binary optimization, and is a problem type traditionally used in computer science. Variables are TRUE and FALSE, states that correspond to 1 and 0 values.

A QUBO problem is defined using an upper-diagonal matrix *Q*, which is an *N x N* upper-triangular matrix of real weights, and *x*, a vector of binary variables, as minimizing the function

where the diagonal terms, * Q_i,i*, are the linear coefficients and the nonzero off-diagonal terms are the quadratic coefficients

**Q_i,j.**This can be expressed more concisely as

In scalar notation, the objective function expressed as a QUBO is as follows:

Read more about QUBO problems and how to formulate them for the D-Wave system here.

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