Please help me construct a graph...

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pernero
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Please help me construct a graph...

Postby pernero » Fri Nov 20, 2009 8:56 pm UTC

I'm not sure if this is the correct board, but here it goes...

I've only ever made simple graphs before. This one requires special computer software.

For now, the problem is simple...

I have derived a formula for a simple model of a star:

[math]P=P_0 (r/r_0)^a[/math] ; [math]T=T_0 (r/r_0)^b[/math]

I need to make a graph of a vs b.

This is where I'm begging you to help me. What (free) program could I use? Could anyone provide instructions on how to graph this with the program?

I thank you very very much in advance!

fazzone
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Re: Please help me construct a graph...

Postby fazzone » Fri Nov 20, 2009 10:11 pm UTC

is http://www.fooplot.com of any help?
*/

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pernero
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Re: Please help me construct a graph...

Postby pernero » Fri Nov 20, 2009 10:26 pm UTC

Thats a neat page. I thank you for it but I'm quite sure I need a program that can plot integrals.

edanite
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Re: Please help me construct a graph...

Postby edanite » Mon Nov 23, 2009 2:27 am UTC

pernero wrote:Thats a neat page. I thank you for it but I'm quite sure I need a program that can plot integrals.


Why do you think you need to be able to plot integrals?

By the way, the problem appears to be under-constrained. Assuming the subscript-zero terms are constant, we still have 5 free variables and only 2 equations which share only one of the variables. Is there something "obvious" that you've left out here?

Think about this: if you assume that all other terms are constant, how are a and b related?

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pernero
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Re: Please help me construct a graph...

Postby pernero » Mon Nov 23, 2009 3:55 pm UTC

In these equations, r is radius, and r0, P0, and T0 are all positive constants. This is keeping in mind that the temperature, pressure, and density all decrease with radius.

After I graph it, I'll have to point out three regions of the graph (convectively stable, unstable and non-physical)

edanite
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Re: Please help me construct a graph...

Postby edanite » Mon Nov 30, 2009 3:41 am UTC

Density wasn't previously mentioned. Can you give an expression that relates the temperature and pressure to the density? (Ideal gas law?) Can you give an expression that relates the density to the radius?

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pernero
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Re: Please help me construct a graph...

Postby pernero » Mon Nov 30, 2009 3:37 pm UTC

After lots of work, I've figured it out. It was much more complex than this. Convection and gas laws had to be taken into account.

Thanks anyways


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