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Messages - Galandros
16
« on: February 01, 2011, 05:01:07 pm »
I really hate monopolists forcing their own crappy prices on the market. That is just greedy. I don't know if this is happening on certain regions or most Canada because it is one of the biggest countries.
The best thing that could happen are companies getting into the market with competitive prices. That is a must for having a fair price and quality of service. But it may be impossible if the monopolists detain all the network infrastructures and rent in such a prize that turns impossible for other companies be competitive.
Offtopic: I also don't like prices too much artificially lower than their real costs because generally it can have very negative impact on nature (except for truly nature-friendly materials of course).
But economy is run by many greedy people, so what could you expect? I hope that there are enough reasonable persons to balance it soon enough for the human and Earth life future.
17
« on: February 01, 2011, 04:45:38 pm »
For doing the opposite you can go the naive or brute force way: calculate catalan numbers until it match (do not forget to handle bad inputs).
I am thinking in a better approach but the factorial is dragging me off.
Offtopic: cool so much recent interest on mathematics here. 
A loop that goes through all of them would be possible, but quite slow :S
Yes, but I can't find any function that is to factorial what logarithm is to exponential. Factorial is also a difficult thing to compute and very easily overflows integer variables. Try 20! and see on how many bits it will fill into. The only thing I could think of is using http://en.wikipedia.org/wiki/Stirling%27s_approximation solve it in order of n. Does it even will work? Maybe only with very large factorials... Still a ugly solution.
18
« on: February 01, 2011, 04:27:39 pm »
Goodness, you really had to do it sometime for real. 
19
« on: January 31, 2011, 09:57:35 am »
No, I didn't used MatLab.
But I guess you won't worry much about it because generally the university provides free licenses to its students for all required software or computers with it. After learning some programming languages, the differences generally are subtle and MatLab seems to be a usual one but more math oriented.
And depends on university and course, sometimes you go straight to other programming language (commonly Java or C).
20
« on: January 31, 2011, 09:52:54 am »
Try scanf("%d",&input);
Note the & as pointer to operator.
21
« on: January 31, 2011, 09:49:20 am »
A switch statement for generating optimized assembly using vector tables would be very used, indeed.
22
« on: January 31, 2011, 09:42:05 am »
Does it exist, if it does, can you tell me?(I need it to do mah APCS Homework  )
No, there isn't any (known) formula to get the sequence of primes. But I don't know if it was proven mathematically that there is not such formula.
The difficulty to crack RSA depends on being hard to find primes and the interest on primes comes also from this.
There are formulas that give asymptotically the average of number of primes in an interval or probability of a random number being prime. See more in:
http://en.wikipedia.org/wiki/Prime_number_theorem
Wait a minute... I can code a program that gets all prime numbers in a second.
For RSA we are talking of numbers with hundreds of decimal digits.
decimal! I thought only integers would take part of such function.
The number of decimal digits representation of the integer. It is true that it is always integer in this sort of things. Don't confuse "decimal type" with its "decimal representation". The RSA public key is 1024-bits to 2048-bits in current days. In general, people understand more the quantities when you mention it in decimal than in binary bits. You barely can imagine the monstrosity of the prime factors...
23
« on: January 31, 2011, 09:28:18 am »
I don't know if I overflowed the irc channel with my posts but I have screenshoots of me filling the new posts completely and possibly near 2 times.
24
« on: January 31, 2011, 09:24:10 am »
Does it exist, if it does, can you tell me?(I need it to do mah APCS Homework )
No, there isn't any (known) formula to get the sequence of primes. But I don't know if it was proven mathematically that there is not such formula.
The difficulty to crack RSA depends on being hard to find primes and the interest on primes comes also from this.
There are formulas that give asymptotically the average of number of primes in an interval or probability of a random number being prime. See more in:
http://en.wikipedia.org/wiki/Prime_number_theorem
Wait a minute... I can code a program that gets all prime numbers in a second.
For RSA we are talking of numbers with hundreds of decimal digits.
25
« on: January 31, 2011, 09:16:33 am »
Yeah that can be useful too. Just make sure to keep old copies for a while, though, in case you accidentally do a backup of a broken file then overwrite the older bug working one..
That happened me once, and hopefully I had a prior backup with a sane copy of the file. I am starting to think to do a CD/DVD/Blu-ray backup of some things that don't get updated for a while and get the disk into a hard box. Because if some file gets corrupt, you miss it and can propagate from there until you cycled your backups and there isn't any good copy of it. And there are a lot of other things, like if you live on an somewhat dangerous area to natural disasters, leave DVDs or a small hard drive if you can afford it, with people of your family living far from you or far away friends of your trust. I think I have everything thought out of my backups. And don't get too much paranoiac, 99% of people just doing a good backup of everything every 3 months and a backup of recent stuff when they accomplished significant progress will never loose considerable amounts of work. Note a good backup is when you have a copy in somewhere independent of where you keep your stuff like two different hard drives on different computers or usb disks. Sorry if my discussion/contribution is going too much in depth but sometimes I enjoy carrying out problems to all possibilities and I thought it was important for me and others trade some opinions in this respect.
26
« on: January 31, 2011, 05:33:51 am »
I am a math major in college and I do plan to go as far as to get a doctorate. I am not 100% sure, but I am fairly certain I will choose a math oriented career such as being a professor.
*By the way, Galandros, I'm Thunderbolt from UTI 
Good luck then. I know because the projects you show off here match those of ThunderBolt in UTI. 
27
« on: January 30, 2011, 06:52:41 pm »
That is okay, I do not know how to properly "write math" yet. But yeah, my goal was to use that to test for primes. I'll look into this when my brain is functioning again, but I think I understand
Incredible how some people come up results already known, independently on math after learning the start of things. And you are on a possible right track, although it gets complicated and you need results like Little Fermat Theorem and Euler's Theorem, many prime testing methods use congruences ideas. I am curious. Are you thinking of following Mathematics to your superior course and career, or keep just as a hobby and possibly work on something related? Remember you are not obligated to answer or reply fast.
28
« on: January 30, 2011, 06:40:23 pm »
That one is interesting, although I haven't fully understand how it can be turing complete. Never thought/read much about it though. Just saw somewhere it was turing complete and I know in a intuitive way what is turing complete.
29
« on: January 30, 2011, 06:36:17 pm »
Okee, here is some food for thought.
(7x-2) mod 9=0 when x=9K-1
K is an integer
This means that all number that can be expressed as 7(9k-1)-2 can always be divided evenly by 9. This isn't really complex, but it is fun if you like prime numbers
So, when:
x=9k-1 (7x-2) mod 9=0 (7x+7) mod 9=0
x=9k-2 (7x-4) mod 9=0 (7x+5) mod 9=0
x=9k-3 (7x-6) mod 9=0 (7x+3) mod 9=0
x=9k-4 (7x-8) mod 9=0 (7x+1) mod 9=0
x=9k-5 (7x-1) mod 9=0 (7x+8) mod 9=0
x=9k-6 (7x-3) mod 9=0 (7x+6) mod 9=0
x=9k-7 (7x-5) mod 9=0 (7x+4) mod 9=0
x=9k-8 (7x-7) mod 9=0 (7x+2) mod 9=0
When I did this, I learned some things about how numbers work. If you wanna have fun, try using values other than 7 and 9. Something this simple can reveal quite a bit about numbers.
Modular arithmetic, it was thought to me and I came up with two independent results: - you can use modular arithmetic to find divisible criteria like you did, here is a simple example: let n be a integer number in decimal form let d(i) be the sequence of its digits in decimal form, i. e., n=sum from i=0 to floor(log(n))+1 of d(i)*10^i or n can be expressed as d(0)+d(1)*10+d(2)*10^2+...+d(n)*10^n then you have 3 divides n if 3 divides sum d(i)*10^i, that is equivalent to sum d(i)*10^i = 0 mod 3 <=> sum d(i)*1^i = 0 mod 3 <=> sum d(i) = 0 mod 3 so, 3 divides n if the sum of digits of n is divisible by 3 Exercises: do the same for 2, 10, 7 or any number you like. - I noted what happened to (x+1)^n mod n when n is prime tips: Pascal triangle, divisibility Note I don't know how to write mathematics in english conventions, I did the best to translate... Also writing in plain text does not help. Sorry if you don't understand but I wrote this quickly.
30
« on: January 30, 2011, 06:23:28 pm »
For doing the opposite you can go the naive or brute force way: calculate catalan numbers until it match (do not forget to handle bad inputs). I am thinking in a better approach but the factorial is dragging me off. Offtopic: cool so much recent interest on mathematics here.
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