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pernero
Posts: 177
Joined: Mon Jun 11, 2007 8:35 pm UTC
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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
Posts: 186
Joined: Wed Dec 10, 2008 9:38 pm UTC
Location: A boat

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

pernero
Posts: 177
Joined: Mon Jun 11, 2007 8:35 pm UTC
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Thats a neat page. I thank you for it but I'm quite sure I need a program that can plot integrals.

edanite
Posts: 56
Joined: Sat Jun 23, 2007 8:32 pm 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?

pernero
Posts: 177
Joined: Mon Jun 11, 2007 8:35 pm UTC
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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
Posts: 56
Joined: Sat Jun 23, 2007 8:32 pm 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?

pernero
Posts: 177
Joined: Mon Jun 11, 2007 8:35 pm UTC
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