In this chapter, we offer advice for dealing with some common problems that you may encounter. We also list and describe the most common mistakes that MATLAB users make. Finally, we offer some simple but useful techniques for debugging your M-files.

Common Problems

Problems manifest themselves in various ways: totally unexpected or plainly wrong output appears; MATLAB produces an error message (or at least a warning); MATLAB refuses to process an input line; something that worked earlier stops working; or, worst of all, the computer freezes. Fortunately, these problems are often caused by several easily identifiable and correctable mistakes. What follows is a description of some common problems, together with a presentation of likely causes, suggested solutions, and illustrative examples. We also refer to places in the book where related issues are discussed.

Here is a list of the problems:

• Wrong or unexpected output

• Syntax error

• Spelling error

• Error or warning messages when plotting

• A previously saved M-file evaluates differently

• Computer won't respond.

Wrong or Unexpected Output

There are many possible causes for this problem, but they are likely to be among the following.

CAUSE: Forgetting to clear or reset variables.

SOLUTION: Clear or initialize variables before using them, especially in a long session.