Summary

To add a new optimization problem to DISCROPT, the user should:

1. Define cost, which computes the objective cost of the solution

2. Define delta_cost, which computes the cost of moving from a solution (with known cost) to a neighbor. This function must be defined so that
   $$cost(ns) = cost(s) + delta\_cost(s, m)$$
   where $ns$ is a neighbor of $s$ obtained by mutating $s$ by $m$.

3. Define delta_extend, which computes the cost of extending a solution (with known cost) to another solution with more more element. This function must be defined so that
   $$cost(ns) = cost(s) + extend\_cost(s, m)$$
   where $ns$ is an extension of $s$ obtained by inserting element $m_e$ into the position $m_p$ of $s$.

4. correctness, which computes the degree of correctness of feasibility of the solution. Users can define it separately on inclusively in cost.

5. delta_correctness, if correctness is defined, this function computes the degree correctness of moving from a solution to a neighbor.

6. extend_correctness, if correctness is defined, this function computes the degree of correctness of extending a solution.