deal.II is a highly sophisticated simulation library based on the method of finite elements. It is developed by professional mathematicians and programmers, and it is open source software. The first question that might arise is why should you use the deal.II library at all. This can be answered with the same argument as the one used for the other software library we have already used. You can, of course, write everything yourself from scratch. However, you only have limited time each day to write your code, and also, you do not want to have just a simple algorithm for a specific problem. You probably want code that is state of the art and very efficient in problem solving. However, not many people would have the knowledge to write highly optimized code and this also takes a very long time. Again, it becomes very clear why deal.II is helpful. It is a complete library already optimized to run on cluster systems and solve different kinds of engineering...