FAQ  •  Login

Mistakes in Course Notes & HW Assignments

<<

Dan Negrut

Global Moderator
Global Moderator

Posts: 833

Joined: Wed Sep 03, 2008 12:24 pm

Unread post Thu Mar 04, 2010 8:29 am

Mistakes in Course Notes & HW Assignments

I'm starting this discussion topic so that people can report here mistakes in the PPT class notes I hand out at the beginning of each lecture.  Also, please post here all the mistakes you find in the text of the homework assignments.
Please do not post here questions, this topics is for mistakes only.

As you post mistakes here I will monitor the discussion thread and comment on whether what you posted was a mistake or not.  In case I confirm that what you found was a mistake and you were the first one to point out the mistake on the forum you will get $1 from me.  I will pay you at the end of the semester.  I hope I don't have to take a second mortgage on the house to pay my debts...
Dan
<<

Dan Negrut

Global Moderator
Global Moderator

Posts: 833

Joined: Wed Sep 03, 2008 12:24 pm

Unread post Thu Mar 04, 2010 12:07 pm

Re: Mistakes in Course Notes & HW Assignments

There was a mistake in the 03/04 slides, specifically slide 8.
As Chris pointed out, the dimension of the partial derivatives with respect to p_i should be 1 by 4 (not 1 by 3), as in the original slides.
The slides uploaded on the website are ok now.
Thank you, Chris.
Dan
<<

ME751Martin

ME751 Student

Posts: 5

Joined: Tue Mar 02, 2010 10:37 pm

Unread post Fri Mar 05, 2010 3:26 pm

Re: Mistakes in Course Notes & HW Assignments

I think I found a mistake worth a dollar :D

Lecture February 18th
Slide 24
Basic GCon: CD

The gamma term is missing the second derivative of the forcing function f(t).

Martin
<<

ME751Anne

ME751 Student

Posts: 28

Joined: Tue Mar 02, 2010 10:14 pm

Unread post Fri Mar 05, 2010 3:32 pm

Re: Mistakes in Course Notes & HW Assignments

Tyler mentioned this to Dan as well.  :(
<<

ME751Martin

ME751 Student

Posts: 5

Joined: Tue Mar 02, 2010 10:37 pm

Unread post Fri Mar 05, 2010 3:40 pm

Re: Mistakes in Course Notes & HW Assignments

Well okay. But I guess it's good to have it written down here as well.
<<

ME751Makarand

ME751 Student

Posts: 5

Joined: Tue Mar 02, 2010 10:38 pm

Unread post Sun Mar 07, 2010 5:25 pm

Re: Mistakes in Course Notes & HW Assignments

<<

ME751Anne

ME751 Student

Posts: 28

Joined: Tue Mar 02, 2010 10:14 pm

Unread post Mon Mar 08, 2010 3:27 pm

Re: Mistakes in Course Notes & HW Assignments

I found a mistake in the lecture slides.


Lecture 10, slide 23, in the gamma equation for the D constraint. It should be d_ij_transpose or the matrix dimensions don't work out.
<<

ME451Tyler

ME751 Student

Posts: 25

Joined: Tue Mar 02, 2010 10:19 pm

Unread post Tue Mar 09, 2010 6:25 pm

Re: Mistakes in Course Notes & HW Assignments

The mistake Makarand pointed out also happens in the 0223 lecture on slide 27.
<<

ME751Martin

ME751 Student

Posts: 5

Joined: Tue Mar 02, 2010 10:37 pm

Unread post Tue Mar 09, 2010 6:32 pm

Re: Mistakes in Course Notes & HW Assignments

Is it okay to claim a dollar from someone who posts a mistake in a mistake?
I found a mistake in the lecture slides.
Lecture 10, slide 23, in the gamma equation for the D constraint. It should be d_ij_transpose or the matrix dimensions don't work out.

Anne, the slide you're talking about is number 21, not 23.
<<

ME451Tyler

ME751 Student

Posts: 25

Joined: Tue Mar 02, 2010 10:19 pm

Unread post Wed Mar 10, 2010 9:14 am

Re: Mistakes in Course Notes & HW Assignments

I need someone to verify this one for me...

Lecture 0225 Slide 9

I think the term dij^T*B(pi,sibar^P) in the last matrix is wrong.  In the second to last, dij^T is multiplied by B(pi,aibar)

Should the second term in the last matrix be (dij^T)*B(pi,aibar)-(ai^T)*B(pi,sibar^P)
<<

Dan Negrut

Global Moderator
Global Moderator

Posts: 833

Joined: Wed Sep 03, 2008 12:24 pm

Unread post Wed Mar 10, 2010 3:24 pm

Re: Mistakes in Course Notes & HW Assignments

Slide 21 of 02/18/2010:
d_ij should indeed be transposed
thank you all.
Last edited by Anonymous on Wed Mar 10, 2010 3:28 pm, edited 1 time in total.
<<

Dan Negrut

Global Moderator
Global Moderator

Posts: 833

Joined: Wed Sep 03, 2008 12:24 pm

Unread post Wed Mar 10, 2010 3:28 pm

Re: Mistakes in Course Notes & HW Assignments

ME751Tyler wrote:I need someone to verify this one for me...

Lecture 0225 Slide 9

I think the term dij^T*B(pi,sibar^P) in the last matrix is wrong.  In the second to last, dij^T is multiplied by B(pi,aibar)

Should the second term in the last matrix be (dij^T)*B(pi,aibar)-(ai^T)*B(pi,sibar^P)


Tyler got this right too.  There should be {\bar {\bf a}}_{i} instead of  {\bar {\bf s}}_{i}^P
<<

ME751Anne

ME751 Student

Posts: 28

Joined: Tue Mar 02, 2010 10:14 pm

Unread post Fri Mar 12, 2010 2:19 pm

Re: Mistakes in Course Notes & HW Assignments

Mistakes in book:

I think Eq. 9.6.21 is incorrect.

Also, Eq. 9.6.22 has incorrect signs.
<<

Dan Negrut

Global Moderator
Global Moderator

Posts: 833

Joined: Wed Sep 03, 2008 12:24 pm

Unread post Fri Mar 12, 2010 7:00 pm

Re: Mistakes in Course Notes & HW Assignments

ME751Anne wrote:Mistakes in book:

I think Eq. 9.6.21 is incorrect.

Also, Eq. 9.6.22 has incorrect signs.


Anne - it depends on how you define i and j.  Also, recall that you have a minus that comes from the fact that you move everything that does not depend on the acceleration in the second derivative of \Phi to the right of the "=" sign

To make a long story short, stick with what we had in the notes, i believe that to be ok.  Did you look at that?
<<

ME751Anne

ME751 Student

Posts: 28

Joined: Tue Mar 02, 2010 10:14 pm

Unread post Sat Mar 13, 2010 7:11 pm

Re: Mistakes in Course Notes & HW Assignments

yes, the book doesn't match how we did it in the notes.
Next

Return to ME751 Spring 2010: Advanced Computational Multibody Dynamics

Who is online

Users browsing this forum: No registered users and 1 guest

cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group.
Designed by ST Software.