4.5 Model the best solution
In moving from the 'possible solutions' to the 'best solution' box, Figure 12, we have to assume that a certain amount of evaluation has been done in the previous loop. The solution is still on paper, and probably not much more than a sketch, but something is badly wrong if the best solution to come forward has not been recognised to be at least feasible in the most basic terms of function, cost and implementation. The next step is to model the solution to estimate how well it will perform. Depending on the subject of the problem, this could take many forms.
The model itself doesn't have to be physical and sometimes a mathematical model can be used. A pretty thorough knowledge of relevant physical properties of real systems, materials and structures is required if a model is to be of any practical use.