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## #1 2013-05-14 17:32:58

ElainaVW
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### Sum this.

Hi;

Fn is the nth Fibonacci number

Last edited by ElainaVW (2013-05-14 17:34:11)

## #2 2013-05-14 17:35:50

bobbym

Online

### Re: Sum this.

Hi;

Please use the latex capabilities of M or the codecogs site for perfect latexing every time.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #3 2013-05-14 18:19:59

anonimnystefy
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### Re: Sum this.

Hi ElainaVW

I am getting

.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

## #4 2013-05-15 20:10:42

ElainaVW
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### Re: Sum this.

Hi anonimnystefy;

Thanks for the kind solutions.

Last edited by ElainaVW (2013-05-15 20:21:46)

## #5 2013-05-15 20:23:27

bobbym

Online

### Re: Sum this.

Hi;

Yes, the integration is too tough. But that is not the only way to skin a cat.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

ElainaVW
Full Member

Offline

## #7 2013-05-17 01:36:01

bobbym

Online

### Re: Sum this.

Hi ElainaVW;

Congratulations on your new member status.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #8 2013-05-17 01:41:15

ElainaVW
Full Member

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### Re: Sum this.

Hi Bobby;

Thanks, I had two of the best there are over here.

## #9 2013-05-17 01:44:56

bobbym

Online

### Re: Sum this.

Hmmmm.

Usually, accelerators like sequences where e is shrinking by a fixed constant.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #10 2013-05-17 02:01:14

Agnishom
Real Member

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### Re: Sum this.

Hi bobbym, How did you do that?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

## #11 2013-05-17 02:07:50

bobbym

Online

### Re: Sum this.

Hi Agnishom;

Bother the OP? It was easy, I am good at being annoying.

But besides from that which do you mean?

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #12 2013-05-19 02:16:14

Agnishom
Real Member

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### Re: Sum this.

The Summation

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

## #13 2013-05-19 06:00:18

bobbym

Online

### Re: Sum this.

Hi Agnishom;

There are many ways to do that sum. When you have the gf you have the sum of the terms of the sequence the gf represents. Normally, the gf is treated formally but when you use it for summation the rules of power series apply,

The numerical way just takes advantage of the double rule and the principles outlined over here.

http://www.mathisfunforum.com/viewtopic … 82#p266682

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #14 2013-05-19 12:27:16

Agnishom
Real Member

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### Re: Sum this.

#### bobbym wrote:

When you have the gf you have the sum of the terms of the sequence the gf represents. Normally, the gf is treated formally but when you use it for summation the rules of power series apply,

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

## #15 2013-05-19 12:34:09

bobbym

Online

### Re: Sum this.

A generating function is nothing more than a power series where we do not care about the usual kaboobly doo called analysis, Radii of convergence, questions of convergence, analytical disks and even what the series converges to do not count.

What is unique about a gf is the coefficients are the number ways of some combinatorics problem. Now, that is very very loose but to show more I would need some examples.

I believe that you asked me a question similar to this one on another forum. It was about partitions, the major reason why Euler helped to invent gf's.

Here we have the gf of the Fibonacci sequence. Want to see how?

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #16 2013-05-19 12:54:42

Agnishom
Real Member

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### Re: Sum this.

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

## #17 2013-05-19 13:06:23

bobbym

Online

### Re: Sum this.

If f(x) = x  / ( 1- x - x^2) then we get:

Recognize those coefficients?

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #18 2013-05-19 13:12:13

Agnishom
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### Re: Sum this.

Yes.

I do not know much about the Taylor series though.
How did you expand that?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

## #19 2013-05-19 13:19:29

bobbym

Online

### Re: Sum this.

That formula up there is the Taylor series. It says that most any function can be converted to and infinite series consisting of powers of x. ( some reservations here but trying to keep it simple and understandable)

For instance:

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #20 2013-05-19 13:34:09

Agnishom
Real Member

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### Re: Sum this.

I entered the following into Maxima and it worked.

#### Code:

`taylor( x  / ( 1- x - x^2), x, 0, 8);`

next...

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

## #21 2013-05-19 13:42:56

bobbym

Online

### Re: Sum this.

Now you are learning!

When there are infinite number of terms we call them a Taylor series when we truncate at say 5 terms then we have a Taylor polynomial.

Now what is so useful about a polynomial instead of the function it replaces? To answer that kind of question you have to know the history of mathematics, something sadly lacking in today's syllabus.

Anyway, if we ever get into the uses of a Taylor series, I mean the real uses not 2 pages devoted to it in some calculus book, then questions of convergence and real analysis apply.

But we are getting away from gf's. You should see the Taylor series has as its coefficients the Fibonacci sequence and they are indexed correctly. We say that x / ( 1- x - x^2) is the generating function of the Fibonacci sequence.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #22 2013-05-19 13:47:50

Agnishom
Real Member

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### Re: Sum this.

We say that x / ( 1- x - x^2) is the generating function of the Fibonacci sequence.

So far, so good...

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

## #23 2013-05-19 13:48:58

bobbym

Online

### Re: Sum this.

Did you understand what I meant when I said indexed correctly?

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #24 2013-05-19 13:50:50

Agnishom
Real Member

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### Re: Sum this.

I overlooked that. Maybe you mean their order?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

## #25 2013-05-19 13:54:15

bobbym

Online

### Re: Sum this.

That is correct.

Notice the first Fibonacci number is 1 and it is the coefficient of x^1. The fourth Fibonacci number is 3 and it is the coefficient of x^4 Likewise, the tenth is 55 and it is the coefficient of x^10.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.