Math 442: Intro to Partial Differential Equations Homework 4
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Homework 4
MATH 442: INTRO TO PARTIAL DIFFERENTIAL EQUATIONS
(Exercises are taken from paTtial DifeTential Equations An IntToduction, second Edition by walter A. strauss.)
1. Let u be a solution to
ut = iuxxx + uxx
with initial condition u(x, 0) = φ(x) on the upper half plane. show that
Repeat the problem for a periodic solution.
2. Exercise &1.3 #6. consider heat low in along circular cylinder where the temperature depends only on t and on the distance T to the axis of the cylinder. Here r = is the cylindrical coordinate. From the three-dimensional heat equation derive the equation ut = k(urr + ur/r).
3. Exercise &2.4 井9. (May use any method). solve the difusion equation ut = kuxx with the initial condition u(x, O) = x2 by the following special method. First show that uxxx satisies the difusion equation with oeTO initial condition. Therefore, by uniqueness, uxxx = O. Integrating this result thrice, obtain u(x, t) = A(t)x2 + B(t)x + C(t). Finally, it,s easy to solve for A, B, and C by plugging into the original problem.
2023-07-24