Highlighting in a formula

In a complex formula or equation, it can be useful to emphasize a specific part. We can achieve this, for example, through highlighting by color or by framing. This is especially useful in presentations, where we could change the highlighted area from frame to frame while explaining.

We will take the challenge to work on more than simple basic math. So we can verify that the method works in arbitrary situations. So our original material will be the amsmath matrices. We will illustrate a matrix transposition by highlighting submatrices and drawing arrows.

How to do it...

We will use TikZ for this. Such a big graphics package may seem to be a bit heavy for such a purpose at first. But it provides us with consistent styles and allows us to do nearly anything graphically.

Let's do an example step by step:

1. Start with a document class:

   \documentclass{article}

2. Load the amsmath package, so we can write matrices:

   \usepackage{amsmath}

3. Load the tikz package:

   \usepackage{tikz}

4. In addition...