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Isn't Calculus just about the greatest thing ever?
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blingdomepiece  





Joined: 03 Aug 2007
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Location: Ottawa ON Canada

PostPosted: Fri Mar 30, 2012 7:01 pm    Post subject: Reply with quote

THABEAST721 wrote:
I am assuming every ball has an equal chance of being selected. The probability of a finite event happening is the size of the event set divided by the size of the sample set. In this case, the event set is the set of picking all six numbers correctly, which only has one occurrence. The sample set is the set of all possible outcomes. This would be 59*58*57*56*55*59 because there are 59 possibilities for the first ball, then 58 for the next, then 57 for the third, then 56 for the fourth, then 55 for the fifth, then the special ball or whatever is in it's own group, so it could be any of the 59 numbers. So calculating that gives your odds of hitting the jackpot to be 1 in 35.4 billion.


I am not familiar with that lottery; in particular I don't know how the special ball works. But for a lottery with five numbers and five balls I think it would be a fairly straightforward calculation; 5/59 * 4/58 * 3/57 * 2/56 * 1/55. You have a 5/59 chance of one of your numbers coming up. If it does, you then have a 4/58 chance of one of your other numbers coming up. And so on, down to the last number. (This works out to 5! * 54! / 59! but I'm too lazy to reverse-engineer the combinatorics... haven't had to care about that stuff for a while).
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bclare  





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PostPosted: Fri Mar 30, 2012 7:52 pm    Post subject: Reply with quote

http://en.wikipedia.org/wiki/Mega_Millions#Playing_the_game

Quote:
Since June 2005, a player picks, or allows the lottery terminal to pick, five different numbers from 1 through 56 (white balls) and one number from 1 through 46 (the Mega Ball number, a gold-colored ball).


Wikipedia is also nice enough to include the calculation (in case you aren't disposed to believe me) that there are (56 choose 5)*(46) = 175,711,536 ticket combinations, so your chance of winning is one in that much. I suppose to most people's understanding of probability it's easier to round to 1 in 200 million.

If anyone's curious, with the current jackpot value of $462m cash, the expected value of buying a ticket is about $2.81; for the annuity payout of ~640m the expected value goes up to $3.82

Tickets cost $1

For cash payout, the expected return on one ticket is over $1 when the jackpot hits about $145 million, although it's only a good investment if you buy a whole lot of tickets, and even then it's a massive longshot because if you don't win the jackpot you get no significant payout (also jackpots this big tend to be split)
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THABEAST721  





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PostPosted: Fri Mar 30, 2012 8:31 pm    Post subject: Reply with quote

Okay well I've never played the lottery, but I guess if those are the numbers then that would change things. But if it is 56 choose 5, that means the order doesn't matter. So choosing the numbers 1 2 3 4 5 would still be a winner if the drawing came up as 5 4 3 2 1. I didn't know it worked that way, but the calculation makes sense if that is the case.

If there are only 175 million possibilities, then it might be plausible to suspect that every combination of numbers has been chosen with so many people playing and a lot of those people playing 10+ tickets.
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bclare  





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PostPosted: Fri Mar 30, 2012 8:55 pm    Post subject: Reply with quote

(I actually this written up before I just looked up the rules of Mega Millions)

Most lotteries I've seen just put the numbers in ascending order, whatever order they were picked in. Makes it easier to tell if your ticket won or not. You could get the same number of ticket combinations with fewer numbers per choice if you did it with order matters.

59 choose 6 (order not important) = 45 million tickets

30 pick 6 (order important) = 42 million tickets
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Vampyromaniac  





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PostPosted: Tue Apr 24, 2012 5:01 pm    Post subject: Reply with quote

I guess this goes into topology a bit but a thought experiment I was doing the other day left me with a pretty cool and surprisingly simple equation. The idea is this: you have two spaceships with a (preferably extremely long) cable of length d connecting them, each one with a perfectly accurate gyroscopic compass (compass as in, it measures angles). You synchronize your compasses so that they're both pointing in the same direction. One spaceship then flies straight forward until the cable is perfectly taut, stops, and engages a rocket on any side of it perpendicular to the cable (left, right, up, or down), flying in an arcing path while keeping the cable taut until it is on the exact opposite side of the stationary spaceship. Then the moving one returns from there straight to the original ship.
Now, the idea is that if our 3-dimensional universe is curved through 4-dimensional space, the (perfectly accurate) gyroscopes will no longer coincide. In fact, it seems reasonable that if the universe was perfectly spherical in that way (and thus, travelling in a straight line long enough would return you to your original position) that you could determine its circumference with simply:
C=4πd/ΔΘ
Where C is the circumference, d is the length of your cable, π is scorehero not being able to display pi, and delta theta (ΔΘ) is the change in angle (in radians, because it's the fucking future). Interestingly, it shouldn't matter if the spaceships are "moving" or not, as long as their motion is perfectly uniform. Also note that this only works if your cable is less than or equal to 1/4 the circumference of the universe (the assumption being that it's actually some ridiculously small percentage of C only calculable because of an impossibly precise gyroscopic compass.)
And ya know, in degrees you could just replace 4pi with 720...
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THABEAST721  





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PostPosted: Fri Apr 27, 2012 5:16 pm    Post subject: Reply with quote

I really hate differential equations (the class) so much. I hope I never have to do anything with them again. My calc 4 class is obviously geared toward engineers and physicists, but for some odd reason they make math majors take the class too. We have not proved a single thing in that class, and my teacher just posts the equations and how to do it... hardly a class fit for a math major.
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louster200  





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PostPosted: Wed May 09, 2012 2:12 am    Post subject: Reply with quote

So, the AB calculus AP test is tomorrow.

brb freaking out.
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yksi-kaksi-kolme  





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PostPosted: Wed May 09, 2012 2:18 am    Post subject: Reply with quote

I am SO FUCKING PUMPED for calc BC tomorrow. I think I've achieved the best level of comfort I need with series for the exam; I know all my convergence tests, Maclaurin series expansions for the functions that the exam focuses on (e^x, cosx, sinx, 1/(1-x)), how to do Taylor series/polynomial approximations of functions (a lot easier than I first thought), finding power series representations of functions, and Taylor remainders. Meanwhile I am very happy with my grasp on the fundamental concepts of calculus, like derivatives and integrals make a ton of sense to me now just looking at a graph and imagining what the function's derivative or integral looks like.

I am ready to get a 5. This is the one AP I truly care about and I am ready to make it happen.
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Vampyromaniac  





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PostPosted: Sat Jun 23, 2012 7:42 pm    Post subject: Reply with quote

bclare wrote:
*thumbs up*

Although the easier way to write what you're saying there would be x^2 - y^2 = (x+y)(x-y)

as in

9*11 = (10-1)(10+1) = 10^2 - 1^1 = 100-1 = 99


It's amazing going back and looking at this post. At the time, I literally thought you were talking about something completely different than I was. I did end up learning some basic calculus after all (because I decided to go back to college) and found out the hard way that I had forgotten pretty much everything past the first half of 9th grade algebra.
It's been fun relearning it though (surprisingly), and I now get excited when I see the clever ways mathematicians can figure out problems, such as Newton's approximation method.

It was also really fun discovering that I had kinda discovered "conjugates" on my own, using patterns in actual numbers instead of algebra with abstract variables... especially since I'm now realizing I'll probably never figure out such a thing again, as I'm exposed to the plethora of mathematical knowledge humanity has already gained. It's amazing how much is out there, and how complex the problems as the cutting-edge are... it seems like you could easily have a bachelor's in mathematics and not even understand what is even being proposed with certain conjectures.

So yeah, I've come to the conclusion that calculus and other branches of mathematics are awesome, even though that probably won't be my college major (I don't have the patience for rigorous proofs... I always just want layman's explanations of what's going on, and it seems like that kind of becomes hard or impossible to come across when you get much more advanced than basic calculus.)

Also: I've watched some college lectures on calculus, and in general it seems to be taught very shittily. Its concepts are really quite simple, but the way it is taught seems to me to be 95% of why it is so difficult and intimidating for those first being exposed to it. Is it really so hard to say that taking the derivative finds the slope of a line whether or not it is curved, or that "dx" represents an extremely small portion of x? I don't think you should be showing students all the equations and proofs before giving them some idea of what it is they're doing when it can so easily appeal to intuition. Just an opinion, and likely a biased one as my interests lie closer to applied maths.
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Sarg338  





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PostPosted: Tue Oct 16, 2012 11:37 pm    Post subject: Reply with quote

Fellow math nerds, I require your help! If I'm asked to find the "Smallest positive root of a funtion f(x)", that just means to find the smallest positive number such that f(number) = 0, correct?

Second part of my question is, I'm suppose to implement this into my program using a "Subinterval Search" method. Not sure if that's a math or Programming term, but does anyone have an idea of what that is? Any specific algorithms I could use?
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Vampyromaniac  





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PostPosted: Wed Oct 17, 2012 8:04 pm    Post subject: Reply with quote

Sarg338 wrote:
Fellow math nerds, I require your help! If I'm asked to find the "Smallest positive root of a funtion f(x)", that just means to find the smallest positive number such that f(number) = 0, correct?

Second part of my question is, I'm suppose to implement this into my program using a "Subinterval Search" method. Not sure if that's a math or Programming term, but does anyone have an idea of what that is? Any specific algorithms I could use?


This probably isn't helpful but it might want you to to find some root at x=a, a>0 and then search for another root at x=b on the interval (0, a), and repeat the process. This is only a guess though.
If you're a clever programmer you can probably set up a while loop to iterate until there is no smaller positive root, then spit out the last (smallest) one it found.
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Sarg338  





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PostPosted: Wed Oct 17, 2012 9:03 pm    Post subject: Reply with quote

Vampyromaniac wrote:
Sarg338 wrote:
Fellow math nerds, I require your help! If I'm asked to find the "Smallest positive root of a funtion f(x)", that just means to find the smallest positive number such that f(number) = 0, correct?

Second part of my question is, I'm suppose to implement this into my program using a "Subinterval Search" method. Not sure if that's a math or Programming term, but does anyone have an idea of what that is? Any specific algorithms I could use?


This probably isn't helpful but it might want you to to find some root at x=a, a>0 and then search for another root at x=b on the interval (0, a), and repeat the process. This is only a guess though.
If you're a clever programmer you can probably set up a while loop to iterate until there is no smaller positive root, then spit out the last (smallest) one it found.


Yeah, talked to him today and that's what he wanted. Start at (0, x), both on the x-axis, and keep getting smaller and smaller until I find it. Obviously the hard part is to figure out a way to implement that as a program, but he said he had a PDF file that would help me a lot, so we'll see! If not, I'll be sure to post here (Instead of the programming thread, since it seems the hard part is figuring out the right algorithm).

It's the calculus part that's gonna be hard. Been a year or so since I've had it. Is there any algorithm that already does this, such as Newton's Algorithm or something to that effect that I could just implement?
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bclare  





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PostPosted: Wed Oct 17, 2012 9:48 pm    Post subject: Reply with quote

Newton-Raphson method could work, depending on what the function is, see http://en.wikipedia.org/wiki/Newton-Raphson#Failure_of_the_method_to_converge_to_the_root

The short answer is that N-R is probably fine though, as long as you've got the derivative easily calculated. You could go even brute-force-r and just fucking plug in values but that's a little inelegant
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Sarg338  





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PostPosted: Thu Oct 18, 2012 4:55 am    Post subject: Reply with quote

Well, my teacher sent me the PDF giving me an example problem and a more in-depth instruction on what I'm suppose to do.

Quote:
Write a program that finds the smallest positive root of the following function:

f(x) = -2 + sin(x) + sin(x^2) + sin(x^3)... + sin(x^1000)

This root is the unique value r between 0 and 1 such that f(r) = 0. The program should divide the interval [0,1] into Several subintervals and create a set of processes or threads, one for each subinterval (Everything in Bold is something I'll have to do later, since the course is Parallel Programming :P). Each process or thread computes the value of f(x) at both ends of its subinterval. One process will find the subinterval where the function changes from negative to positive. The algorithm should then iterate, dividing this subinterval into pieces and assigning these new smaller pieces to the various processes (or threads). When the subinterval size becomes less than 10^-11, the programm should terminate, printing the root of the function


Ignore anything that mentions splitting it up. That comes later and I'm only working on the serial version at the moment. Obviously, and you guys know this, i don't want it done for me by you guys.

My initial plan to this is to try and computer it for just -2 + sin(x) + sin(x^2). If that comes up with the right answer, then it should come up with the right answer, no matter how many iterations I do, correct?
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bclare  





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PostPosted: Thu Oct 18, 2012 5:08 am    Post subject: Reply with quote

So, split up [0,1] into 10 subintervals, width 0.1. Check which interval(s) have roots in them, then take the lowest one of those and divide it into 10 subintervals, etc. Terminate after 11 steps.
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