MA3304 Methods of Applied Mathematics 2020/21
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2020/21
MA3304
Methods of Applied Mathematics
Formulae
Power series
Definite integral
Perturbation Expansions
Trigonometric Identities
1. (a) Show that one of the roots of the equation
where > 0 is a small parameter is given by
Determine the leading two terms in the asymptotic expansions of the other two roots.
(b) Find the first three terms in the expansion
of the solution of the differential equation
where u(0) = 1 and 0 < << 1.
(c) Solve the Fredholm integral equation
where m and n are non-negative integers and find the eigenvalues of the associated
homogeneous equation.
(d) Reformulate the following boundary value problem
with y(0) = 1, y'(1) = 0, as an equivalent integral equation in the form
where f (x) and K(x, s) should be specified.
(e) Consider the problem of minimising the functional
in the set of admissible functions
Write down the Euler-Lagrange equation and determine the only solution u to this equation in the set A.
2. (a) Use Laplace’s method to obtain the leading term in the asymptotic expansion as x → o of the following integral
Provide justifications for any approximations that you use to derive the result. [10] (b) Consider the following initial value problem
where 0 < < 1 is a small parameter with
Use the Poincar´e-Linstedt method to show that a uniformly valid expansion of the solution to this problem is given by
where
3. (a) Consider the Fredholm integral equation
i. Use the method of successive approximations to generate a Neumann series approximation to this equation that is valid for |λ| < A where A needs to be determined.
ii. Calculate the first three iterated kernels and determine an expression for the resolvent kernel. Hence derive a closed from expression for the solution of the equation.
(b) Find the eigenvalues and eigenfunctions of the integral equation
where f (x) and g(x) are real-valued continuous functions satisfying
With reference to these integral properties, explain why f (x) and g(x) are linearly independent.
4. Consider the problem of minimising the functional:
over the set of admissible functions
(a) Write down the weak Euler-Lagrange equation for the minimisation problem as- sociated with the functional.
(b) Find the solution for the corresponding Euler-Lagrange equation.
(c) Write the second variation of the functional.
(d) Explain why the solution of the Euler-Lagrange equation obtained in part (b) of the question is a weak local minimiser by solving the corresponding Jacobi equation. Refer to any relevant theorems that you use.
(e) Find the solution of the Euler-Lagrange equation from part (b) of the question if the set of admissible functions is replaced by
2022-01-14