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visits member for 3 years, 5 months
seen Jul 21 at 17:43

Oct
17
comment Self Study in Dynamical Systems
Unfortunately, the link you've provided appears to be broken.
Aug
11
comment Recommendation for a book and other material on dynamical systems
I just ran across this course, for others who are interested: youtube.com/watch?v=mkfU9zVNGkQ&feature=relmfu
Jun
28
comment Online tools for doing symbolic mathematics
+1, this looks like an interesting tool.
Jun
27
comment Online tools for doing symbolic mathematics
It's as though everything lately has been telling me to learn Python. +1 for answering with precisely what I asked for: a web-based app that provides symbolic manipulation that isn't limited to one-liners.
Jun
22
comment Using differentials
@Noteventhetutorknows - The fractional notation helps give the notion of rates, but it also gives the impression you can just do normal algebraic manipulations on them -- which is definitely not true. It can be done, as Americo Tavares points out, but it must be done very carefully and rigorously.
Jun
22
comment Using differentials
+1 because it has the potential to generate answers to help explain proper use of differentials.
Jun
22
comment Using differentials
@Theo - That's fine. What affect does \$\$ have?
Jun
22
comment Using differentials
@Noteventhetutorknows - re: dubiousness, I was specifically referring to the homogeneous equation I wrote, but what you wrote is fraught with what I would consider to be inappropriate manipulations. The chain rule gives: $\frac{dy}{dx} = \frac{dy}{dt}\frac{dt}{dx}$. Nothing about the chain rule says it's safe or valid to swap denominators as though $\frac{dy}{dt}$ is a simple fraction.
Jun
22
comment Using differentials
Agreed. When I took my ODE class I just went with it, but as I went back and worked through some of that material years later it occurred to me that the homogeneous equation above is actually a partial differential equation in disguise, of sorts -- hence my addendum with $\frac{dy}{dt}$ (etc). Adding $t$ explicitly seemed to make it easier to 'guess' the solution for those problems.
May
16
comment Convolution & DFTs: How much zero padding is necessary to avoid circular convolution?
@joriki - Very good point, thank you. If you want to provide the correct answer and that note as part of your answer, I'll accept it.
May
16
comment Convolution & DFTs: How much zero padding is necessary to avoid circular convolution?
Scratch that. The answer is $2N - 1$ along each dimension. See the following: cnx.org/content/m10963/latest
Apr
21
comment Is this a positive semi- definite matrix
The OP didn't ask about 2x2 matrices.
Apr
21
comment The 9 Billion Names of God
Although this is an interesting experience, the format of your question is very open-ended. There's no way anyone can give a 'right' answer, and often no answer is selected to be accepted for open-ended questions.
Apr
20
comment Maximization of Two Areas — Calculus 1
I'm a little unsure how to pull this off without another constraint. It seems like a circle is the most efficient shape in terms of containing the most area, so any expression you come up with would force the square's perimeter to zero and give you a circle with circumference = 10 meters.
Apr
19
comment how do you solve $y''+2y'-3y=0$?
@night - That notation is not at all uncommon. I've encountered it in 3 texts for undergrad study, and it's one of the most useful techniques discussed in the differential equations "Problem Solvers" book -- with plenty of examples given, albeit more awkwardly typed.
Apr
12
comment Genetic Algorithms
The next step will be to choose something you want to encode for the algorithm to work with. The two most obvious (only?) things you can model (or use to model) are actions to take within the game, and current/previous game state/actions. One way to handle it could be to use your genetic sequence to weight how important information is about current/previous game states and previous moves, then use some type of weighted sum to determine future moves. The paper you linked to probably describes the encoding they used.
Apr
12
comment Geometric Series - Simple Question
If it's a calculation you want to verify, just plug it into wolframalpha.com
Apr
8
comment Rules of Division
@Bill - Well put.
Apr
8
comment Rules of Division
@Bill - No. You made a good argument for a more general treatment of the topic. I'm arguing that there should be a "simplified" treatment as well. My point about the math jargon was to make the point that it doesn't need to be only readable by someone who has a desire to invest themselves in math enough to understand the more general/rigorous treatment.
Apr
8
comment Rules of Division
@Bill - That's an excellent point, but in this case the OP needed it for the GRE. One of the more frustrating things for me 'growing up' in math was trying to digest material in Mathworld and Wikipedia math entries -- mostly because they were loaded with math jargon I was unfamiliar with. If someone's studying for the GRE, they shouldn't have to know a lot of math jargon just to learn a couple of divisibility tests.