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 11-17-2004, 06:22 AM #1 darkRoom Member   Registered: Mar 2004 Location: Valencia, espaņa Distribution: Slack, Gentoo, Custom Posts: 162 Rep: please help me do maths :) Hi Its funny how you can completely avoid doing any maths despite programming everyday. Anyway i need to learn a bit of maths but its been a long time, can anyone explain how to calculate the sum below ? N is any number entered. E is the mathematical symbol 'sum of' (whats this sign called? it will aid future googling N E (i+2) i=1 Sorry about the formatting . . . The problem is that i don't know what to do with the 'i' and what is this type of maths called so i can do a search and find resources, also does anyone know any good resources for boolean algebra ? Thanking you all kindly
 11-17-2004, 06:39 AM #2 rjlee Senior Member   Registered: Jul 2004 Distribution: Ubuntu 7.04 Posts: 1,991 Rep: The greek E-like letter you refer to is a sigma.
 11-17-2004, 08:18 AM #3 acid_kewpie Moderator   Registered: Jun 2001 Location: UK Distribution: Gentoo, RHEL, Fedora, Centos Posts: 43,417 Rep: you mean what does it actually mean? it means the sum of all values of i+2 where i is between 1 and N e.g. N = 4 answer is (1+2) + (2+2) + (3+2) + (4+2) = 3 + 4 + 5 + 6 = 18
 11-17-2004, 12:34 PM #4 darkRoom Member   Registered: Mar 2004 Location: Valencia, espaņa Distribution: Slack, Gentoo, Custom Posts: 162 Original Poster Rep: Thanks acid_kewpie, Perhaps with the answer i could of guessed that one, but i only had the sum and no answer. Anyone with good links (boolean algebra, boolean logic, karnaugh maps) please feel free post
 11-18-2004, 10:05 AM #5 darkRoom Member   Registered: Mar 2004 Location: Valencia, espaņa Distribution: Slack, Gentoo, Custom Posts: 162 Original Poster Rep: Maths tutorials are so bad, i got to get me a book. But in the meantime i got another one n is any number and i don't understand the relevance of X0. Its newtons algorithm to calculate a square root. So if n = 4, answer = 16 but how to work the answer out ?? X0 = 1 Xi = 0.5 * (N / Xi-1 + Xi-1) Thanks for the help
11-18-2004, 10:09 AM   #6
bakery2k
Newbie

Registered: Oct 2003
Posts: 0

Rep:
Quote:
 Originally posted by darkRoom How to work the answer out ?? X0 = 1 Xi = 0.5 * (N / Xi-1 + Xi-1)
Substitute for i.

X1 = 0.5 * (N / X0 + X0)
X2 = 0.5 * (N / X1 + X1)
...

 11-18-2004, 11:50 AM #7 darkRoom Member   Registered: Mar 2004 Location: Valencia, espaņa Distribution: Slack, Gentoo, Custom Posts: 162 Original Poster Rep: I still don't get it, are you sure X2 is really neccessary to calculate the answer ?
 11-19-2004, 12:58 AM #8 gorzuate LQ Newbie   Registered: Apr 2004 Location: IN Distribution: Gentoo Posts: 9 Rep: In case you're curious, your first problem is a summation and is solved like this: N E(i + 2) i = 1 breaks down into: Code: ```N N E(i) + E(2) = N(N+1)/2 + 2N i = 1 i = 1``` You could find summations in any Calculus book or by googling for summations: http://www.google.com/search?q=summations For your second problem, using 4 as an example isn't a good idea. It's better to use 2. Or 3. And then you can see that you indeed need to go all the way to X2 (in the case of 2) or X3 (in the case of 3). Last edited by gorzuate; 11-19-2004 at 01:20 AM.
 11-19-2004, 02:23 AM #9 floppywhopper Member   Registered: Aug 2004 Location: Albany, Western Australia Distribution: Mageia 4, Debian 8, SME 9, IP Fire, PCLinuxOS, LinuxMX Posts: 629 Blog Entries: 2 Rep: omg this will be the second book I've recommended in as many days maybe we should link to Hari's Book site just kidding Mods Never was that good at maths, my old maths teacher will confirm that. However during my accounting studies we had to use a text book even I could follow. it is ... Business Maths and Statistics by Peter Waxman ISBN 0 7248 0138 3 pub by Prentice Hall your first formula looked similar to one we use to calculate compounding interest. Anyway I dont know whether you'll be able to buy it outside Australia, but you could try Amazon. hope this helps live long and prosper floppy
 11-19-2004, 08:32 AM #10 Winno Member   Registered: Sep 2003 Location: Australia Distribution: Fedora Core 3 / Mandrake 10.1 / Gentoo 2005.0 Posts: 100 Rep: With reference to Newton's method, it is iterative (repetitive, ie X2, X3, X4). The answer usually gets better and converges. But it's not failsafe. It fails when there's no answer or results diverge.
11-21-2004, 12:18 AM   #11
LQ Newbie

Registered: Nov 2004
Location: Sliven, Bulgaria
Distribution: SuSE 9.0
Posts: 5

Rep:

Quote:
 Originally posted by darkRoom Hi Its funny how you can completely avoid doing any maths despite programming everyday. Anyway i need to learn a bit of maths but its been a long time, can anyone explain how to calculate the sum below ? N is any number entered. E is the mathematical symbol 'sum of' (whats this sign called? it will aid future googling N E (i+2) i=1 Sorry about the formatting . . . The problem is that i don't know what to do with the 'i' and what is this type of maths called so i can do a search and find resources, also does anyone know any good resources for boolean algebra ? Thanking you all kindly
The name of the Summation sign (your E) is the Greek Letter "Sigma". For those who don't know, it looks like the number 3 backwards, and all 4 arms straight lines.

Of course, when you get into Calculus, the Sigma becomes the Integration Sign. But whatever terrible things happen in your life caused by Calculus serves you right!

 03-15-2005, 03:28 PM #12 radostsguy LQ Newbie   Registered: Nov 2004 Location: Sliven, Bulgaria Distribution: SuSE 9.0 Posts: 5 Rep: Σ! There it is! In Windoze, you just need to install the Greek Alphabet, which is very easy. (Don't ask me hhow to do it in Linux, but I'm sure you know how!) Then it's the letter "B" on your English Language Keyboard.
03-15-2005, 04:43 PM   #13
PTrenholme
Senior Member

Registered: Dec 2004
Location: Olympia, WA, USA
Distribution: Fedora, (K)Ubuntu
Posts: 4,186

Rep:

Quote:
 Originally posted by darkRoom Hi Its funny how you can completely avoid doing any maths despite programming everyday. ...
You don't say which language you use for programming, but -- to pick a simple one -- what you're looking at is a "for" loop. In this case: (This is psudo-code, buut you should 'get it.')
Code:
```Sum := 0
for i = 1..N
Sum := Sum + i + 2
next
print Sum```
For the other example:
Quote:
 X0 = 1 Xi = 0.5 * (N / Xi-1 + Xi-1)
Code:
```X := N/4
while (X != 1)
Y := 0.5 * (N/(X - 1) + X-1)
if  abs(X - Y) < 0.00001 break
X := Y
next
print Y```
Generally, most simple maths expressions are almost directly expressable in computer code.

(In fact, the APL computer language was designed as a mathematical language for stating proofs before it was implimented as a computer code. But that's off the subject here.)

Hope this helps.

 03-15-2005, 06:31 PM #14 jaz LQ Newbie   Registered: Apr 2004 Location: midwest Distribution: fedora core 1 Posts: 12 Rep: maths?
 03-16-2005, 03:47 AM #15 radostsguy LQ Newbie   Registered: Nov 2004 Location: Sliven, Bulgaria Distribution: SuSE 9.0 Posts: 5 Rep: Yeah! maths! You know, that subject that is easy until one hits Differential Equations?

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