Math Is Fun Forum

lindah

Member

Registered: 2010-01-25

Posts: 121

Moment Generating Moment

http://img819.imageshack.us/i/57381179.png/

Hi guys,

May I confirm if the MGF I have derived is correct?

My answer after:

Thanks
Lin

Last edited by lindah (2011-06-07 21:57:27)

gAr

Member

Registered: 2011-01-09

Posts: 3,482

Re: Moment Generating Moment

Hi lindah,

I get the same.

Expectation is:

Last edited by gAr (2011-06-07 21:02:46)

---

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

lindah

Member

Registered: 2010-01-25

Posts: 121

Re: Moment Generating Moment

I've got my exam tomorrow, so thank you for taking the time to give feedback on this one!!!

The algebra/working was very messy.

Last edited by lindah (2011-06-07 21:17:21)

gAr

Member

Registered: 2011-01-09

Posts: 3,482

Re: Moment Generating Moment

You're welcome.
But which algebra was messy?

All the best for your exams.

---

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

lindah

Member

Registered: 2010-01-25

Posts: 121

Re: Moment Generating Moment

But which algebra was messy?

Sorry, it wasn't a reference your workings!!
The question on the paper says its worth 2 marks, for all the working (I used integration by parts and quotient rule for the derivative)

May I ask how you took the limit? Is it L'Hopitals rule?

gAr

Member

Registered: 2011-01-09

Posts: 3,482

Re: Moment Generating Moment

Oh, okay.

If it's out of 100, 2 marks is a little less I guess.
I used a CAS to get the derivative and the limit.

And yes, if I'm not using a computer, I'd use L'Hôpital's rule.

---

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

lindah

Member

Registered: 2010-01-25

Posts: 121

Re: Moment Generating Moment

Thank you very much  for clarifying!!

gAr

Member

Registered: 2011-01-09

Posts: 3,482

Re: Moment Generating Moment

You're welcome!

---

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

lindah

Member

Registered: 2010-01-25

Posts: 121

Re: Moment Generating Moment

I used a CAS to get the derivative and the limit.

And yes, if I'm not using a computer, I'd use L'Hôpital's rule.

Hi
Thanks for this, up to this point I had only used Mathematica as CAS software.
I started using Matlab and got this. All this time I'd been performing this work by hand. Good news is I can bring a laptop to my exam.

gAr

Member

Registered: 2011-01-09

Posts: 3,482

Re: Moment Generating Moment

Hi lindah,

Good news is I can bring a laptop to my exam.

With mathematica?!
It can do most of the things for you!

---

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

lindah

Member

Registered: 2010-01-25

Posts: 121

Re: Moment Generating Moment

Hi lindah,

Good news is I can bring a laptop to my exam.

With mathematica?!
It can do most of the things for you!

Yes, I've installed Mathematica (for a regression question using matrices in the exam) and Matlab for finding derivatives.
I tried putting the question I asked in this thread through Mathematica, but it didn't seem to be able to process it.
With Matlab I obtained the same answers as you!

gAr

Member

Registered: 2011-01-09

Posts: 3,482

Re: Moment Generating Moment

Mathematica wasn't able to process something, and matlab got it? Strange, Which question?

Mathematica can do derivatives too.

---

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

lindah

Member

Registered: 2010-01-25

Posts: 121

Re: Moment Generating Moment

Hi gAr,

I've just tried Mathematica again and got the answers. I must have defined too many symbolic relations (I had many notebooks open last time I tried it).

I've just defined

f[t_] := ((3 t - 1) E^t + (1 - t) E^-t)/(4 t^2)
f'[t] // Simplify
m=f'[t]
Limit[m, t->0]

This is great for me, because the output from Mathematica is much easier to read than Matlab's

gAr

Member

Registered: 2011-01-09

Posts: 3,482

Re: Moment Generating Moment

Hi lindah,

Glad that you got it now!

---

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."