Math 551 Section 01 Summer Session 1 2022
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
Math 551 Section 01
Summer Session 1 2022
Chapter 3 Homework
1. (10 points) Consider a function f given by
f (x) = coshx + cos x _ γ,
where γ is a parameter and takes the values of γ = 0, 1, 2, 3. Make a graph of the function f (x) for each value of γ on the interval [_3, 3] and determine whether f (x) has a root. To do so, you have to check the criteria required by the Intermediate Value Theorem. Then, using the file “bisect.m”, approximate the root with absolute tolerance 10-10 for the value of γ that f (x) does have a root. Include a copy of the graph of f (x) for the respective cases and MATLAB output.
2. Assume the following fixed point iterations x首+1 = g(x首 ): (a) (8 points) x首+1 = _16 + 6x首 + with x* = 2, (b) (9 points) x首+1 = x首 + with x* = 31/3 ,
(c) (8 points) x首+1 = with x* = 3,
where x* corresponds to the respective fixed point.
Then, which of the above iterations will converge to the fixed point x* indicated above, provided that x0 s x* , i.e., the initial iterate x0 is sufficiently close to x* ? If it does converge, then find the order of convergence.
Hint: You need to use the definition of the rate of convergence where you must exam- ine the derivatives of g(x) at x* . Furthermore, make sure to check that x* is indeed a fixed point!
3. (20 points) Using the m-file “fixed point.m”, find the three roots of ez _ 2x2 = 0,
with |x首+1 _ x首 | < 10-10 as a convergence criterion. Note that plotting will help here. Furthermore, explain your choices for the g(x) utilized in order to ensure convergence.
4. Consider Newton’s method for finding +lα with α > 0 by finding the positive root of f(x) = x2 _ α = 0. Assuming that x0 > 0, show the following:
(a) (5 points)
x首+1 = ╱x首 + x首(α) 、,
(b) (5 points)
x首(2)+1 _ α = ╱ xx首(_)α 、2 ,
for k > 0 and therefore x首 > lα for k > 1.
5. (10 points) Perform three iterations of Newton’s method by hand (i.e., with a calcu- lator) for the following function:
f(x) = x _ e-z , x0 = 1.
6. (15 points) Assume that f e C3 [a, b] and there is a root x* e [a, b] such that f(x* ) =
0 and f/ (x* ) 0. Show that Newton’s method converges quadratically.
7. (10 points) Perform three steps of the secant method for f(x) = x3 _ 2, using x0 = 0, x1 = 1.
2022-06-05