Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

478 Chapter 15 MATLAB

The M-file

As explained previously, for simple operations you can use MATLAB’s Command Window to

enter variables and issue commands. However, when you write a program that is more than a

few lines long, you use an M-file. It is called an M-file because of its .mextension. You can cre-

ate an M-file using any text editor or using MATLAB’s Editor/ Debugger. To create an M-file,

open the M-file Editor by going to File SSNew SSBlank M-File, and MATLAB opens a new

window in which you can type your program. As you type your program, you will notice that

MATLAB assigns line numbers in the left column of the window. The line numbers are quite

useful for debugging your program. To save the file, simply click File SSSaveAs...and type

in the file-name. The name of your file must begin with a letter and may include other char-

acters such as underscore and digits. Be careful not to name your file the same as a MATLAB

command. To see if a file-name is used by a MATLAB command, type exist (‘file-name’)in

the MATLAB’s Command Window. To run your program, click on Debug SSSave File and

Run(or use the function key F5). Don’t be discouraged to find mistakes in your program the

first time you attempt to run it. This is quite normal! You can use the Debugger to find your

mistakes. To learn more about debugging options, type help debugin the MATLAB Command

Window.

Example 15.3 It has been said that when Pascal was 7 years old, he came up with the formula to

determine the sum of 1, 2, 3,... , through n. The story suggests that one day he was asked by

his teacher to add up numbers 1 through 100, and Pascal came up with the answer in few

minutes. It is believed that Pascal solved the problem in the following manner:

First, on one line he wrote the numbers 1 through 100, similar to

1234........... 99100

Then, on the second line he wrote the numbers backward

100 99 98 97........... 2 1

Then, he added up the numbers in the two lines, resulting in one hundred identical values

of 101

101 101 101 101........... 101 101

Pascal also realized that the result should be divided by 2 — since he wrote down the numbers

1 through 100 twice — leading to the answer: Later, he generalized his

approach and came up with the formula

n 1 n 12

2

.

10011012

2

5050.

n 1 n 12

2

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