Differential under an integral sign.

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SUMMARY

The discussion centers on the application of the Leibniz rule for differentiating under an integral sign, specifically when dealing with a function y(x) and a function R(y). The key takeaway is the necessity of evaluating the functional derivative, which involves assessing how the integral changes with an infinitesimal variation in y(x). Additionally, boundary conditions are crucial for solving variational problems, particularly in the context of Hamilton's principle.

PREREQUISITES
  • Understanding of the Leibniz rule for differentiation under the integral sign
  • Knowledge of functional derivatives and their applications
  • Familiarity with variational calculus and Hamilton's principle
  • Basic concepts of chain rule in calculus
NEXT STEPS
  • Study the application of the Leibniz rule in various integral contexts
  • Learn about functional derivatives and their significance in calculus of variations
  • Research boundary conditions in variational problems, particularly in Hamiltonian mechanics
  • Explore examples of differentiating under the integral sign with varying functions
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Mathematicians, physicists, and students engaged in advanced calculus, particularly those focusing on variational methods and differential equations.

binbagsss
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Sorry I'm not sure how you get math script on here, so have had to attach it.

It is a differential under an integral sign and I'm not too sure how to approach it.
Would you use Leibniz rule?
Do you differentiate or integrate first?
- where y is a function of x, and R of y

Thanks in advance
 

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You don't need to integrate here.

You have y as a function of x and R as a function of y. You want to find the partial of R with respect to y which you know is a function of x. So when you differentiate the integrand, don't forget to apply the chain rule.
 
No! What's asked for is the functional derivative. You get it by evaluating, how the integral changes when the function y(x) changes by an infinitesimal \delta y(x). Unfortunately the problem is not completely stated. You also need boundary conditions. If it's a usual variational problem like in Hamilton's principle, the values at the end points are fixed.
 

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