# MA213: Numerical Analysis

Unit 3: Nonlinear Equations of a Single Real Variable   From the very first algebra course you took, you have been asked to “find x” for many different problems.  You will now learn how to pass that task on to the computer!  You might not be surprised to know that there are slow-and-sure methods as well as fast-and-risky methods.  We will develop tools that allow us to measure just how fast a given method converges to an answer.  Some methods are best only in specialized situations, and some work well generally or in combination with others.  Finally, we will write programs to compare both the safest and fastest of our methods.

Unit3 Learning Outcomes
Upon successful completion of this unit, the student will be able to:
- Understand the method of bisection, Newton’s method and the secant method for solving equations in one real variable.  - Be able to compare and contrast these methods with respect to several distinctive properties, and construct a hybrid method possessing desirable properties of each.

3.1 Roots of Nonlinear Equations   - Reading: University of Arkansas: Mark Arnold’s “Solving Equations in one Real Variable”

``````Link: University of Arkansas: Mark Arnold’s “[<span
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(PDF)

Instructions: Click on the link above, then select the appropriate

This resource should take approximately 1 hour to complete.

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3.2 The Method of Bisection   - Reading: University of Arkansas: Mark Arnold’s “Bisection” Link: University of Arkansas: Mark Arnold’s “Bisection” (PDF)

Instructions: Click on the link above, then select the appropriate link to download a pdf of the reading. Although it may not be clear yet, the method of bisection has some exceptional properties.  The fact that it can give us an upper bound on the error at each iteration is one such property.  The price we pay is a relatively slow speed of convergence and the need to begin with a root bracketing interval.  There is not much to analyze in this method, our fundamental computation is to compute the sign of f(p) correctly, where p=(a+b)/2.  Now it turns out that it is better to compute p as p=a+(b-a)/2.  Why?

This resource should take approximately 1.5 hours to complete.

Instructions: Click on the link above, then watch the video lectures in the chapter listed above.  In this case there are 4 lectures that have been split into 4 videos.

This resource should take approximately 40 minutes to complete.

3.3 The Newton-Raphson Method   - Reading: University of Arkansas: Mark Arnold’s “Newton’s Method” Link: University of Arkansas: Mark Arnold’s “Newton’s Method” (PDF)

Instructions: Click on the link above, then select the appropriate link to download a pdf of the reading. So here is a classic and very simple use of the idea of linearization.  At each step we replace f(x) with the line tangent to f at (x_p, f(x_p)).  The new iterate x_{p+1} is simply the root of that tangent line.  This method can be very fast, but is can also fail.  Can you think of two ways it can fail?

This resource should take approximately 1 hour to complete.

Instructions: Click on the link above, then watch the video lectures in the chapter listed above.  In this case there are 6 lectures that have been split into 9 videos.

This resource should take approximately 1 hour to complete.

3.4 The Secant Method   - Reading: University of Arkansas: Mark Arnold’s “The Secant Method” and “Newton & Secant Example” Link: University of Arkansas: Mark Arnold’s “The Secant Method” (PDF) and “Newton & Secant Example” (PDF)

Instructions: Click on the link above, then select the appropriate link to download a pdf of the reading. Carefully read the pdf’s.  The secant method is a Newton-like method that is general purpose.  It is arguably faster than Newton’s method, but like Newton’s method, can fail.

This resource should take approximately 1.5 hours to complete.

Instructions: Click on the link above, then watch the video lectures in the chapter listed above.  In this case there are 3 lectures that have been split into 4 videos.

This resource should take approximately 1/2 hour to complete.

3.5 Order of Convergence   - Reading: University of Arkansas: Mark Arnold’s “Order of Convergence”, “Convergence of Newton’s Method” and “Convergence of the Secant Method” Link: University of Arkansas: Mark Arnold’s “Order of Convergence” (PDF), “Convergence of Newton’s Method” (PDF) and “Convergence of the Secant Method” (PDF)

Instructions: Click on the link above, then select the appropriate link to download a pdf of the reading. Carefully read the pdf’s.  There is a lot in this section.  The idea of linearization we now associate with a Taylor polynomial.  The definition of order of convergence is worth putting to memory, and it is as easy as “the new error is approximately a constant times the old error raised to the alpha”.  If we have superlinear convergence, then we also have a useful (but not guaranteed) error estimate.  In light of this, you should think about how you could determine when to stop a Newton or secant iteration.  If someone said that Newton’s method was faster than the secant method, would you agree?  How would you argue your point?

This resource should take approximately 4 hours to complete.

3.6 Hybrid Methods   - Reading: University of Arkansas: Mark Arnold’s “Hybrid Methods for Root Finding” Link: University of Arkansas: Mark Arnold’s “Hybrid Methods for Root Finding” (PDF)

`````` Instructions: Click on the link above, then select the appropriate
There are other hybrid methods for the root finding problem.   The
reading presents a simple example.  Construct a list of what
properties your ideal method would have.  Does bisection combined
with secant possess all of your properties?  Where (if at all) does
this method fall short?

This resource should take approximately 2 hours to complete.

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Instructions: Click on the link above, then watch the video lectures in the chapter listed above.  In this case there is 1 lecture that has been split into 3 videos.

This resource should take approximately 45 minutes to complete.

3.7 Programming Case Study: Compare Bisection and Secant   - Reading: University of Arkansas: Mark Arnold’s “Bisection and Secant” Link: University of Arkansas: Mark Arnold’s “Bisection and Secant” (PDF)

This resource should take approximately 4 hours to complete.

3.8 Of Things Not Covered   - Reading: University of Arkansas: Mark Arnold’s “Roots of a Polynomial” and “Example of a Bad Polynomial” Link: University of Arkansas: Mark Arnold’s “Roots of a Polynomial" (PDF) and Example of a Bad Polynomial” (PDF)

Instructions: Click on the link above, then select the appropriate link to download a pdf of the reading. Maybe you have already thought of alternatives to Newton’s or the secant method.  There are alternatives.  When higher higher order derivatives are available, or when we know that a function is smooth enough, we can use polynomials of higher order (like Mueller’s method).  We can also use quadratic interpolation with the roles of x and y reversed; this is called inverse quadratic interpolation… There are many methods, even for problems with only one unknown variable; imagine what’s waiting to be invented for f(x_1,x_2,…,x_n)=0?  Even for a polynomial function of 1 variable, finite precision arithmetic can make for challenging computational problems; the example in the reading is an ill posed polynomial root finding problem.

This resource should take approximately 1 hour to complete.

`````` Instructions: Carefully answer the two questions in this