New to the method of steepest descent

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SUMMARY

The discussion centers on the application of the method of steepest descent to the integral of the function \(\int_{-\infty}^{+\infty} dx e^{\frac{ax^{2}}{2}}e^{\ln[2\cosh(b+cx)]}\). The user has identified the saddle point but is uncertain whether to expand the \(x^2\) term or the \(\ln(\cosh)\) term. They have opted to work with the \(\ln(\cosh)\) function and calculated its second-order Taylor series but are unclear on the next steps, particularly regarding the integration process and the potential need for complex variable substitution.

PREREQUISITES
  • Understanding of the method of steepest descent
  • Familiarity with Taylor series expansions
  • Knowledge of complex variables and their applications in integration
  • Experience with hyperbolic functions, specifically \(\cosh\)
NEXT STEPS
  • Study the method of steepest descent in detail, focusing on complex variable integration
  • Learn about Taylor series expansions for hyperbolic functions, particularly \(\cosh\)
  • Research the implications of saddle points in the context of steepest descent
  • Explore examples of integrals involving products of exponential functions and their expansions
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Students and researchers in mathematics and physics, particularly those working with complex integrals and approximation methods, will benefit from this discussion.

Beer-monster
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Homework Statement



I'm new to this approximation method and was wondering the best way to proceed with this function:

[tex]\int_{-\infty}^{+\infty} dx e^{\frac{ax^{2}}{2}}e^{ln[2cosh(b+cx)]}[/tex]

I've found the saddle point (I think). But I was wondering if it would be best to expand the x squared term or the ln(cosh) term. If the latter, should I expand the cosh as a taylor series to get ln(expanded cosh) and then expand the logarithm (of the expanded cosh?) and simplify the result?.

Thanks for your help.
 
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Sorry--I'm not quite sure what the problem you're trying to answer is.
 
I'm not quite sure how to integraye this function using the method of steepest descent. Usually you have a function of a complex variable, which this is not.

And often examples show only one exponential function where I have a product of two, so I'm not 100% which is the more rapidly varying one (i.e. which function do I expand as a Taylor series).

I went ahead and worked with the ln(cosh) function, and calculated its derivatives to get the Taylor series to 2nd order. Now I'm not sure how to move forward? Do I just integrate or do I need to substitute complex variables?
 

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