<a name="Intro"></a>
<h1>Introduction</h1>
+Since this is the first tutorial program, let us comment first on how
+this tutorial and the rest of the deal.II documentation is supposed to
+work. The documentation for deal.II comes essentially at three
+different levels:
+- The tutorial: This is a collection of programs that shows how
+ deal.II is used in practice. It doesn't typically discuss individual
+ functions at the level of individual arguments, but rather wants to
+ give the big picture of how things work together. In other words, it
+ discusses "concepts": what are the building blocks of deal.II and
+ how are they used together in finite element programs.
+- The manual: This is the documentation of every single class and
+ every single (member) function in deal.II. You get there if, for
+ example, you click on the "Main page" or "Classes" tab at the top of
+ this page. This is the place where you would look up what the second
+ argument of Triangulation::create_triangulation_compatibility means,
+ to give just one slightly obscure example. You need this level of
+ documentation for when you know what you want to do, but forgot how
+ exactly the function was named, what its arguments are, or what it
+ returns. Note that you also get into the manual whenever you read
+ through the tutorial and click on any of the class or function
+ names, i.e. the tutorial contains a great many links into the manual
+ for whenever you need a more detailed description of a function or
+ class. On the other hand, the manual is not a good place to learn
+ deal.II since it gives you a microscopic view of things without
+ telling you how a function might fit into the bigger picture.
+- Modules: These are groups of classes and functions that work
+ together or have related functionality. If you click on the
+ "Modules" tab at the top of this page, you end up on a page that
+ lists a number of such groups. Each module discusses the underlying
+ principles of these classes; for example, the @ref Sparsity module
+ talks about all sorts of different issues related to storing
+ sparsity patterns of matrices. This is documentation at an
+ intermediate level: they give you an overview of what's there in a
+ particular area. For example when you wonder what finite element
+ classes exist, you would take a look at the @ref fe module.
+
+
+
In this first example, we don't actually do very much, but show two
techniques: what is the syntax to generate triangulation objects, and
some elements of simple loops over all cells. We create two grids, one