/// <summary>
/// Add a node that we would like as close to position i as possible, with the requested weight.
/// </summary>
/// <param name="id">Caller's unique identifier for this node</param>
/// <param name="position">Desired position</param>
/// <param name="weight">The weight of the corresponding term in the goal function</param>
public void AddVariableWithIdealPosition(int id, double position, double weight)
{
// This throws an ArgumentException if a variable with id is already there.
variables.Add(id, solver.AddVariable(id, position, weight));
}