math section revision

[jessdtate]

update and revise math section. Update with the following criteria:

• General clarity Update Fwd/Inv toolkit document #12 General clarity edits to toolkit document #23
• updated algorithms and examples update algorithms and feature descriptions in toolkit doc #20
• update screenshots Update screenshots in fwd/inv document #19
• include literature citations include literature citations in toolkit doc #22
• Add conceptual diagrams add diagrams for clarity of descriptions #21
• unify math notation unify math notation in toolkit documentation #24