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MathGroup Archive 1998

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RE: Differential Equation evaluation



  Your equation seems to lead to a solution that in many cases tends to 
infinity at the infinity, so it is very unlikely you can set a
condition  like f'[Infinity]==0
                                       2 eq = ((f')')'[x] + f[x] f'[x] +
1 - f'[x]  == 0 DSolve[eq, f, x]
bc0 = f[0] == 1 && f'[0] == 1 && (f')'[0] == 1 sol = NDSolve[eq && bc0,
f, {x, 0, 30}, MaxSteps -> 100000] g = f /. sol[[1,1]]
Plot[g[u], {u, 0, 30}]

Hope this helps,


----------------------------------------------- Jean-Marie THOMAS
Conseil et Audit en Ingenierie de Calcul www.cybercable.tm.fr/~jmthomas
------------------------------------------------


-----Message d'origine-----
De:	Spooky [SMTP:SLKBC@cc.usu.edu]
Date:	dimanche 22 fevrier 1998 20:55 A:	mathgroup@smc.vnet.net
Objet:	[mg11085] Differential Equation evaluation


	Hi, I am new to Mathematica and just bought verison 3.0, I am trying to
solve a differential equation of the form:

F''' + F*F' + 1 - (F')^2 == 0

with boundry conditions for F, F', F'' at 0 and F' at infinity, is there
a way to handle this?  When I try this, if I include that boundry
condition at infinity  with the others, Mathematica tells me I have to
many constraints, if I leave it off I can solve it, if I leave off the
condition for F' at 0, it tells  me it can't find the value of variable
at the variable at 0.  So, my question, is how do I handle this in
Mathematica.

I have another general question about the system.  I am using version
3.0 for Win95.  Often, if I make a syntax error, Mathematica will print
me an error message but then I can't be certain that any subsequent
error messages are valid.  The reason I say this is that I  will find
my error, correct it and then I will get another error message upon
evaluation.  After struggling with it for  a while, I will close it and
re-enter and what gave me errors prior to re-entering, evaluate fine.
Is there some way to be sure that  the errors are valid?

Thanks for all of your help.

Shayne C. Rich
SLKBC@cc.usu.edu




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