please help me do maths :)

darkRoom · 11-17-2004, 06:22 AM

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

rjlee · 11-17-2004, 06:39 AM

The greek E-like letter you refer to is a sigma.

acid_kewpie · 11-17-2004, 08:18 AM

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

darkRoom · 11-17-2004, 12:34 PM

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

darkRoom · 11-18-2004, 10:05 AM

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

bakery2k · 11-18-2004, 10:09 AM

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)
...

darkRoom · 11-18-2004, 11:50 AM

I still don't get it, are you sure X2 is really neccessary to calculate the answer ?

gorzuate · 11-19-2004, 12:58 AM

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).

floppywhopper · 11-19-2004, 02:23 AM

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

Winno · 11-19-2004, 08:32 AM

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.

radostsguy · 11-21-2004, 12:18 AM

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!

radostsguy · 03-15-2005, 03:28 PM

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.

PTrenholme · 03-15-2005, 04:43 PM

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.

jaz · 03-15-2005, 06:31 PM

maths?

radostsguy · 03-16-2005, 03:47 AM

Yeah! maths!

You know, that subject that is easy until one hits Differential Equations?