Lab 8—The Matlab Debugger

Purpose

This lesson gives you a basic ability to use Matlab’s debugger.

Background

A debugger is a programming tool that lets you interact with a program while it executes: monitor the values of variables, watch the program execute line by line, etc. Matlab has an easy-to-use debugger for functions and scripts. I will demonstrate some of this debugger’s features in class on November 30.

Activity

Some of you noticed that the bisection function you developed for lab 7 gives you an unexpected answer of 0 if you ask it to find the x coordinate for the closest point on the peninsula in the interval [-2,2]. This answer appears incorrect because visually the closest points ought to have x coordinates near -2 or 2. Such a situation—an unexpected and seemingly incorrect result from a program—is exactly what debuggers are meant to help programmers sort out.

Use Matlab’s debugger to explore the behavior of your bisection function when asked to find a root of the derivative of the lab 7 distance function in the interval [-2,2]. In particular, use the debugger to…

• Find out how many times the main loop in your function executes,
• Find the values of x_l, x_u, and their midpoint during these executions of the loop, and
• Find out which arms of the if statement inside the main loop execute.

Follow-Up

I will grade this exercise in a face-to-face meeting with you. However, you do not have to schedule a separate meeting for this exercise—we can discuss it briefly during your next meeting with me for grading some other exercise.