Assignments: Unless specifically stated otherwise, we encourage collaboration on assignments, provided (1) you spend at least 15 minutes on each and every problem alone, before discussing it with others, and (2) you write up each and every problem in your own writing, using your own words, and understand the solution fully. Copying someone else's work is cheating (see below), as is copying the homework from another source (e.g., prior year's notes, etc.). The quiz problems will often be very similar to the assignment problems; if you truly understand the assignments, then the quizzes will be easy.
Quizzes and final exam: A quiz is a short exam—no collaboration or discussion is permitted. If you have a question during a quiz, ask the instructor.
Cheating is a very serious offense. If you are caught cheating, you can expect a failing grade and initiation of a cheating case in the University system. Basically, cheating is an insult to the instructor, to the department and major program, and most importantly, to you and your fellow students. If you feel that you are having a problem with the material, or don't have time to finish an assignment, or have any number of other reasons to cheat, then talk with the instructor. Just don't cheat.
To avoid creating situations where copying can arise, never e-mail or post your solution files in public directories. You can post general questions about interpretation and tool use but limit your comments to these categories. If in doubt about what might constitute cheating, send the instructor e-mail describing the situation.