Function Introduction Exercises

by Albert Ticona Jr.

In programming, often you would see a list of lines or phrases on a file that when you execute it, it somehow performs a specific task. How do they do it? Well all of these lines and phrases execute a certain purpose such as displaying a message, calculate the average of a data set, or any other tasks that can be done by a computer. In Matlab, if you type display(“Hello World”) on the window, the message “Hello World” will be printed below the command window. The combinations of all those phrases will ultimately execute the task that the “program” was asked to do. In order to execute a certain overall task in a program, you have to break the task into parts such that each different part performs different parts of the program's main task. Sometimes certain tasks are repeated in a program several times, taking up a lot of space. In this case, it would be simple to write this sub-task separately from the program and then type a command in the main program that executes the sub-task from its separate location. For example, suppose you wanted to write a program that wanted to calculate the average over five data sets. One part of this program would be to find the total sum of the data for each data set. One could simplify the program by writing a separate function that calculates the total sum in a separeate location. Then one would only need to write the “shortcut” command five times in the main program. In structured programming, we refer to this as creating a function, and the command that executes the function from within the main program is called a function call. MATLAB has a call for most elementary functions (if not all). Some examples include the exponential function, the trigonemetric functions (sine and cosine), and some special ones such as the sync function. Polynomial functions can be easily defined in MATLAB, almost the same way you would when writing them down on your algebra homework. A list of MATLAB functions can be found if you enter the command:

doc functions

and then go under Functions-- Aphabetical list. If you're not sure, whether a function is defined as a MATLAB function, you can always find out online either www.mathworks.com or just Googling it. Commonly used ones are: sin(x), cos(x), tan(x), acos(x), asin(x), atan(x), exp(x), sind(x) ( returns the sine value for a value expressed in degrees), sqrt(x), etc. As we saw earlier display() is itself a function that displays what ever value that is placed within the parantheses. The syntax for calling any function in MATLAB is: function_name(parameter) The parameter is the input required by the function in order to return a result, which in most cases is just a number or a vector of numbers. Usually if you omit the semi-colon after the function call, the result will be displayed on the MATLAB screen. Examples of Matlab Functions:

display(sin(pi)); % will display the sine value of pi (pi being in unit radians)
ans =

   1.2246e-16

display(acos(1/2)); % will display the arc cosine value of 1/2
ans =

    1.0472

display(exp(1)); % will display the value of the natural number e
ans =

    2.7183