Learning Objectives

At the end of this class you should be able to

• Use fprintf to display text messages in the command window
• Use fprintf for display formatted values of numeric variables in the command window
• Write a for loop to traverse a vector
• Recognize an if-end construct (more practice later)

Reading

• Chapter 2, pp. 57 - 76
• Chapter 8, pp. 179 - 182

For a gentle introduction to fprintf, try this screencast by Robert Talbert.

Lecture Slides

Download

• Notes on Using fprintf
• Large size image of Figure 1 in the "Using fprintf" notes.
• Slides on the fprintf command
• Slides on for loops
• Slides on the if constructs

Comments on lecture content

We more carefully discuss the fprintf statement for displaying structured output to the command window. You have seen fprintf in some of the sample codes and now it's time to learn how to use it.

It is strange and surprising that the textbook does not mention fprintf and focuses instead on disp. The fprintf command is much more versatile than the disp command. The syntax of the fprintf command also takes some practice to master. However, the pay-off is great for creating flexible and well-formated output.

The for loop structure is used to repeat a sequence of calculations. We will use for loops whenever we can't write vectorized expressions. What are vectorized expressions? Here is an example of a vectorized expression on the left, and a for loop on the right.

% -- Vectorized                   % -- Explicit loop
x = linspace(0,2*pi);             x = zeros(1,100);        % preallocate for efficiency
y = sin(x);                       y = zeros(1,100);
                                  dx = 2*pi/(length(x)-1);
                                  for i = 1:length(x)
                                     x(i) = (i-1)*dx;
                                     y(i) = sin(x(i));
                                  end

Clearly the vectorized version is more compact and easy to grasp. That doesn't mean for loops are bad.

The if-end, if-else-end and if-elseif - else - end structures are used to take actions depending on conditions that are determined while the code is running. Both for loops and if structures are essential tools in writing MATLAB code to do numerical analysis.