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### Topics - Brian Bi

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##### Ch 9 / 9.3 problem 18
« on: March 25, 2013, 12:32:43 AM »
I'm having some trouble getting this problem to work out. There are four critical points: (0,0), (2, 1), (-2, 1), and (-2, -4). At the critical point (-2, -4), the Jacobian is \begin{pmatrix} 10 & -5 \\ 6 & 0 \end{pmatrix} with eigenvalues $5 \pm i\sqrt{5}$. Therefore it looks like it should be an unstable spiral point. However, when I plotted it, it looked like a node. Has anyone else done this problem?

http://www.math.psu.edu/melvin/phase/newphase.html

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##### MAT 244 Misc / How are bonus points counted?
« on: February 08, 2013, 01:26:10 AM »
The marking scheme says there's some bonus mark $B = \min(B_{class} + B_{web}, 6)$ where $B_{class}$ and $B_{web}$ are between 0 and 4. Does this mean that additional karma beyond 4 doesn't count toward bonus marks? Or does $B_{web}$ not correspond exactly to the number of karma points you have? (I don't want to "unnecessarily" deprive other people of the opportunity to be the first to post solutions to problems.)

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##### Technical Questions / Preview
« on: February 01, 2013, 10:44:54 AM »
The preview post feature doesn't work at all. It just gets stuck at "Fetching preview..."

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##### MAT 244 Misc / Re: Bonus problem of the week 1:
« on: January 15, 2013, 01:29:51 AM »
Submitting (first) the correct solution of the "Problem of the Week" (I will try to post them each week) you get karma which translates to bonus marks.
Is there any predictability as to when in the week you intend to post them, or should we just sit here and refresh the forum constantly?

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##### MAT 244 Misc / Comparison of 9th and 10th textbook editions
« on: January 06, 2013, 05:43:03 PM »
Hi all,

I'm looking for a volunteer---someone who has already bought the 10th edition of the textbook, or will do so shortly---who will meet me weekly, or bi-weekly, or however often problem sets are posted, so we can compare problem numbers between the 10th edition and the 9th edition (which I already have).

If I am able to get a volunteer, I will post corresponding problem numbers in this thread after each time we meet. This way, other students who already have the 9th edition, or can obtain it much more cheaply than the 10th, won't have to buy another edition of the textbook just so they can do the problems.

I'm sure people would give you karma for it  (which means bonus marks apparently)

Thanks!

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