Links to source tikz code for each respective diagram can be found by clicking the figure caption.
I thought this diagram may come in handy sometime:
Although figure 2 seems elementary, I wanted to have it posted some where for quick reference
Note: for images like figure 3, I’ll try to upload corresponding 3D graphs for each class (e.g., figure 4 at the origin would correspond to a a saddle). Ill probably type up a blog post on this particular diagram in the near future!