MAE 4730/5730, Intermediate Dynamics,  Cornell

Homework policy: To get credit, please do these things on each homework.

a) Hand in in at the start of class on the due date. Unless stated otherwise, homework will be due at least 6 days after it is posted.  Late (1 minute or 2 months) homework will be accepted for reduced credit. More late, more reduction. Contact your grader to figure out how to turn in late homework.

b) On the first page of your homework, please put the following to ease sorting:

 On the top left corner Please put a staple, e.g.: On the top right corner Neatly print your name, course, date, e.g.: Very good, even excellent, and .... more than needed (real example). Sally Golnaraghi MAE 4730 or 5730  HW 1, Due date

c) As noted above, please, at home, put a Staple at the top left corner. Folded interlocked torn corners fall apart. Paperclips fall off.

d) Cite your help. At the top of each problem clearly acknowledge all help you got from TAs, faculty, students, or any other source (with exceptions for lecture, text and section, which need not be cited). You could write, for example: "Mary Jones pointed out to me that I needed to draw the second FBD in problem 2." or "Nadia Chow showed me how to do problem 3 from start to finish." or "I copied this solution word for word from Jane Lewenstein " or "I found a problem just like this one, number 386.5.6, at cheatonyourhomework.com, and copied it." etc. You will not lose credit for getting and citing such help. Don't violate academic integrity rules: be clear about which parts of your presentation you did not do on your own. Violations of this policy are violations of the Cornell Code of Academic Integrity.

e) Every use of linear or angular momentum balance must be associated with a clear correct free body diagram.

f)
Your vector notation must be clear and correct.

g)
Every line of every calculation should be dimensionally correct (carry your units, read  the section on units in the Ruina/Pratap books).

h)

i) Some problems may seem like make-work because you already know how to do them. If so, you can get 90% credit by writing in full "I can do this problem but don't feel I will gain from writing out the solution" or, in short, "Can do, don't want to." You can keep doing this unless/untill your grader/TA challenges your self-assessment.

j) Computer work should be well commented. Your name should be near the top of the computer text file. Before handing in, you should highlight (or circle with a colored pen) your name on the computer printout. At least some part of any other computer output should also include your name, printed by the computer. Highlight (or circle) your name on each page.

k) Grading and regrading. So long as you have made a good attempt at your first effort, you can get 90% credit by redoing a problem with 1 week of when it is returned to you.

l) Hold on to your homework. We may not record grades correctly as we go. At the end of the semester you we may ask you to hand in a folder of your completed HW.

Study advice: Try to do assigned homework problems from beginning to end with no help from book, notes, solutions, people, etc., yourself without looking up even one small thing. Explain, at least outloud to yourself, every step. If you did need help, then afterwards start the problem over by yourself without looking up even one small thing. Then similarly do other problems that are like the assigned problems. Then do old prelims and exams. Finally, for A+ style studying, invent and solve your own problems.

# Checklist for  homeworks

When doing a problem, and afterwards, please go down this check-list before handing in your work.  If there is any small part of this that you do not understand, ask  in class or in office hours.

GENERAL

Make it so that when you pick up your homework in 10 years,  with no access to the syllabus or the assignments, you will, as easily as possible, understand the question, understand your answer, and believe your answer.   That is your goal. All else is subservient to that.

MATLAB

1. Derivations.  Show hand calculations for derivation of equations of motion. Or, equivalently, show clear computer algebra inputs and outputs.

2Print out.  Print and attach the entirety of the code you use.  Well commented internally and with additional hand-written annotations, as needed.

3. Verify.   Show, by whatever combination of methods you have the ability and time for, the reasons you think your solution is correct.  Some ideas:
a) matches an analytic solution.
b) A special case matches an analytic solutions.
c) Obeys one or another known and applicable symmetry or conservation law.
d) Matches intuitive trends.
Use figures and numerical values for these purposes.

4. Answer the question. Your work should show the answer clearly.  Assume we don't trust you. Usually you want to use figures to show the result.  And words.  And, if appropriate, numbers.

5. Label plots.  Each plot needs axis labeled and a title.  In a pinch you can add these by hand.

6.   Axis equal.  If both axis represent physical position, unless you have good reason to do otherwise, use  Matlab's "axis equal".  This way circles will look round, squares square, and trajectories will have the right shapes.

As a general rule your computer code should not be written in code.  Rather, each line should be readable and checkable.  In ODE problems, always do the following.

a. Use clear variables.  Unpack variables and constants into readable variables. No calculations should be done with, for example, z(4) and z(7). Using readable variables makes the code 100 times more readable and debuggable.

b. Structs.  Pass parameters using structs.  Namely p.m, p.G etc, not a list of variables.

8. Don't throw in a random use of Euler's method.  If you are solving your ODEs with, say, ODE45,  then also use ODE45 for your energy check by adding equations like \dot W = P to your list of ODEs.

9. Black and white.  You can use color.  But your plots need to make sense when printed in black and white.  So use, say, thick red lines and thin blue lines.

10.  tspan.   Unless all you want is the solution at the final time, always use something like

tspan = linspace(0,10,1001),  rather than
tspan=(0,10).  That way you get output at times you care about.

11. Options.  Appropriately use these features of ODESET:   'reltol', 'abstol', 'events'.