Appoximate a non-analytical function?

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The discussion focuses on the approximation of non-analytic functions near a point and the criteria for determining the analyticity of solutions to ordinary differential equations (ODEs) and partial differential equations (PDEs). Key references include the Picard–Lindelöf theorem for ODEs and a connection to Hilbert's 19th problem regarding the analyticity of solutions in the calculus of variations. The conversation highlights the limitations of Taylor series for certain infinitely differentiable functions and seeks methods for effective approximation in these cases.

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  • Understanding of non-analytic functions
  • Familiarity with ordinary differential equations (ODEs) and partial differential equations (PDEs)
  • Knowledge of Taylor series and their limitations
  • Basic concepts of the calculus of variations
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  • Research the Picard–Lindelöf theorem for ODEs
  • Explore Hilbert's 19th problem and its implications for analytic solutions
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  • Study the calculus of variations and its relation to regularity of solutions
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Mathematicians, physicists, and engineers interested in the approximation of complex functions, as well as researchers working on differential equations and their solutions.

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Appoximate a non-analytic function?

Dear all,

is there a way to do that near a point?

Also, for a given ODE or even PDE, is there a criterion to show whether its solution is analytic? Is it a proper question in fact?

Thanks!
 
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Not sure what you mean about approximating a non-analytical function near a point. It depends what you mean, and what the function is. Is it continuous? And are you only concerned about numerics here - or what is the context?

Regarding the DE/PDE's here's a starting point for you:

http://en.wikipedia.org/wiki/Picard–Lindelöf_theorem

If you ever find a way to do it in general for PDE's, you're a genius.
 
Thanks you for your reply. Basically my second question turned out to be partly a rephrase of Hillberts 19th problem as I just found out:

"Are the solutions of regular problems in the calculus of variations always analytic?"
Here is an overview http://math.univ-lyon1.fr/~clarke/Clarke_Regularity.pdf

The first question: for a certain type of functions Taylor series do not work at some points even though they are infitely differentiable there like this one
http://planetmath.org/?op=getobj&from=objects&id=3081
So the question is is there a method to approximate such a function near a point still.
 

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