2002年《科学与工程人员基础MATLAB指南》

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《2002年Essential MATLAB for Scientists and Engineers》是一本由Brian Hahn编著的专业教材，专为科学家和工程师设计，旨在介绍MATLAB这一强大的数值计算和数据分析工具的基础知识。本书版权属于Elsevier Inc., 并受到严格的版权保护，未经许可不得复制或传输。该书共分为两部分：Part I - Essentials，以及后续章节。Part I 开篇即介绍了"Getting going"，旨在帮助读者快速入门。在第一章，"1.1 Introduction"部分，作者会概述MATLAB的历史背景、目标用户群以及软件在科学研究和工程中的核心作用。这部分可能包括MATLAB的版本信息（如ISBN 978-0-7506-5240-3），强调它作为一款高度灵活且直观的编程环境，能够简化数学运算、数据可视化和算法实现。随后，"1.2 Using MATLAB"章节会详细介绍如何启动MATLAB，如何创建和管理变量，以及基本的数据类型和数据结构。读者将学习如何使用MATLAB的工作区、命令窗口以及脚本编辑器进行交互操作。这部分内容对于初次接触MATLAB的新手来说至关重要，因为它是理解和掌握MATLAB操作流程的基础。书中后续章节可能会深入探讨MATLAB的核心功能，如矩阵运算、函数和子程序的编写、图形绘制、数据处理、信号处理、线性代数、优化算法等，这些都是科学和工程领域广泛应用的MATLAB技术。此外，书中还可能包含案例研究和实际应用示例，帮助读者更好地理解和应用MATLAB解决实际问题。通过阅读这本书，读者不仅能掌握MATLAB的基本操作，还能了解如何高效地利用其高级特性来提升科研和工程项目的效率。在版权页上，作者提醒读者若需进一步获取使用授权，应直接联系Elsevier的 Science & Technology Rights Department 获取许可，以便遵循版权法规。《2002年Essential MATLAB for Scientists and Engineers》是一本实用的教程，适合想要提升MATLAB技能的专业人士和学生，通过系统学习，他们能更深入地理解和掌握这个强大的数学工具。

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MATLAB fundamentals

Objectives

The objectives of this chapter are to introduce you to some of the fundamentals of MATLAB pro-

gramming, including:

• various MATLAB desktop and editing features;

• variables, operators and expressions;

• vectors (arrays);

• basic input and output;

• repetition (for);

• decisions (if).

By now you will probably be wanting to use MATLAB to solve problems of your own. In this chapter

we will look in detail at how to write MATLAB statements to solve simple problems. There are two

essential requirements for successful MATLAB programming:

• You need to learn the exact rules for writing MATLAB statements.

• You need to develop a logical plan of attack for solving particular problems.

This chapter is devoted mainly to the ﬁrst requirement: learning some basic MATLAB rules. Computer

programming is a precise science (some would say it is also an art); you have to enter statements

in precisely the right way. If you don’t, you will get rubbish. There is a saying among computer

programmers:

Garbage in, garbage out.

If you give MATLAB a garbage instruction, you will get a garbage result.

Once you have mastered the basic rules in this chapter, you can go on to more interesting and substantial

problems. But ﬁrst we need a quick tour of the MATLAB desktop.

MATLAB fundamentals 11

2.1 The MATLAB desktop

The default MATLAB desktop is shown in Figure 1.1. It should immediately be stressed that MATLAB

has an extremely useful online Help system. If you are serious about learning MATLAB you should make

it your business to work through the various Help features, starting with the section on the desktop.

To get into the Help browser, either expand the MATLAB item in the Launch Pad and click on Help,

or click on the help button (?) in the desktop toolbar, or select the Help menu in any tool. Having

opened the Help browser, select the Contents tab in the Help Navigator pane on the left. To get to the

desktop section expand successively the MATLAB, Getting Started and Development Environment

items. MATLAB Desktop is listed under the latter. When you’ve looked at the Desktop item you should

go on to Desktop Tools. (If you mess up your desktop and want to get back to the default, select the

View -> Desktop Layout -> Default menu item.)

The desktop contains a number of tools. We have already used the Command Window. On the left is

the Launch Pad, which shares a ‘docking’ position with the Workspace browser (underneath the Launch

Pad in the default). Use the tabs to switch between the Launch Pad and the Workspace browser. Below

the Launch Pad you will ﬁnd the Command History, sharing with the Current Directory browser.

You can resize any of these windows in the usual way. A window can be moved out of the MATLAB

desktop by undocking it. Do this either by clicking on the arrow in the window’s title bar, or by making

the window active (click anywhere inside it) and then selecting Undock from the View menu.

To dock a tool window that is outside the MATLAB desktop (i.e. to move it back into the desktop)

select Dock from its View menu.

You can group desktop windows so that they occupy the same space in the MATLAB desktop. Access

to the individual windows is then by means of their tabs. To group windows in this way drag the title bar

of one window on top of the title bar of the other window. The outline of the window you’re dragging

overlays the target window, and the bottom of the outline includes a tab. The Status bar informs you to

Release the mouse button to tab-dock these windows. If you release the mouse the

windows are duly tab-docked in the outlined position.

There are six predeﬁned MATLAB desktop conﬁgurations, which you can select from the View ->

Desktop Layout menu.

2.2 Programs

In Chapter 1 we saw some simple examples of how to use MATLAB, by entering single commands

or statements at the MATLAB prompt. However, you might want to solve problems which MATLAB

can’t do in one line, like ﬁnding the roots of a quadratic equation (and taking all the special cases into

account). A collection of statements to solve such a problem is called a program. In this section we look

at the mechanics of writing and running two short programs, without bothering too much about how they

work—explanations will follow in the rest of the chapter.

Cut and paste

Suppose you want to draw the graph of e

−0.2x

sin(x) over the domain 0 to 6π , as shown in Figure 2.1.

The Windows environment lends itself to nifty cut and paste editing, which you would do well to master.

Proceed as follows.

From the MATLAB desktop select File -> New -> M-ﬁle, or click the new ﬁle button on the desktop

toolbar. This action opens an Untitled window in the Editor/Debugger. You can regard this for the time

being as a ‘scratch pad’ in which to write programs. Now type the following two lines in the Editor,

exactly as they appear here:

x = 0 : pi/20 :6*pi;

plot(x, exp(-0.2*x) .* sin(x), ’r’),grid

Incidentally, that is a dot (full stop, period) in front of the second * in the second line—explanation

later! The additional argument ’r’ for plot will draw a red graph, just to be different.

12 Essential MATLAB for Scientists and Engineers

0 2 4 6 8 101214161820

−0.4

−0.2

0.2

0.4

0.6

0.8

Figure 2.1 e

−0.2x

sin (x)

Next, move the mouse pointer (which now looks like a very thin capital I) to the left of the x in the

ﬁrst line. Keep the left mouse button down while moving the mouse pointer to the end of the second

line. This process is called dragging. Both lines should be highlighted at this stage, probably in blue, to

indicate that they have been selected.

Select the Edit menu in the Editor window, and click on Copy (or just use the keyboard shortcut

Ctrl+C). This action copies the highlighted text to the Windows clipboard, assuming that your operating

system is Windows.

Now go back to the Command Window. Make sure the cursor is positioned at the  prompt (click

there if necessary). Select the Edit menu, and click on Paste (or use the Ctrl+V shortcut). The contents

of the clipboard will be copied into the Command Window. To execute the two lines in the program,

press Enter. The graph should appear in a ﬁgure window.

This process, from highlighting (selecting) text in the Editor, to copying it into the Command Window,

is called ‘cut and paste’ (more correctly ‘copy and paste’ here, since the original text is copied from the

Editor, rather than being cut from it). It’s well worth practising until you have it right.

If you need to correct the program, go back to the Editor, click at the position of the error (this

moves the insertion point to the right place), make the correction, and cut and paste again. Alternatively,

you can use command-line editing to correct mistakes. As yet another alternative, you can paste from

the Command History window (which incidentally goes back over many previous sessions). To select

multiple lines in the Command History window keep Ctrl down while you click.

If you prefer, you can enter multiple lines directly in the Command Window. To prevent the whole

group from running until you have entered the last line use Shift+Enter or Ctrl+Enter after each line

until the last. Then press Enter to run all the lines.

As another example, suppose you have $1000 saved in the bank. Interest is compounded at the rate

of 9 per cent per year. What will your bank balance be after one year? Now, if you want to write a

MATLAB program to ﬁnd your new balance, you must be able to do the problem yourself in principle.

Even with a relatively simple problem like this, it often helps ﬁrst to write down a rough structure plan:

1. Get the data (initial balance and interest rate) into MATLAB.

2. Calculate the interest (9 per cent of $1000, i.e. $90).

3. Add the interest to the balance ($90 + $1000, i.e. $1090).

4. Display the new balance.

MATLAB fundamentals 13

Go back to the Editor. To clear out any previous text, select it as usual by dragging (or use Ctrl+A),

and press the Del key. By the way, to de-select highlighted text, click anywhere outside the selection

area. Enter the following program, and then cut and paste it to the Command Window.

balance = 1000;

rate = 0.09;

interest = rate * balance;

balance = balance + interest;

disp( ’New balance:’ );

disp( balance );

When you press Enter to run it, you should get the following output in the Command Window:

New balance:

1090

Saving a program: script ﬁles

We have seen how to cut and paste between the Editor and the Command Window in order to write and

run MATLAB programs. Obviously you need to save the program if you want to use it again later.

To save the contents of the Editor, select File -> Save from the Editor menubar. A Save ﬁle as:

dialogue box appears. Select a directory and enter a ﬁle name, which must have the extension .m,in

the File name: box, e.g. junk.m. Click on Save. The Editor window now has the title junk.m. If you

make subsequent changes to junk.m in the Editor, an asterisk appears next to its name at the top of

the Editor until you save the changes.

A MATLAB program saved from the Editor (or any ASCII text editor) with the extension .m is called

a script ﬁle,orsimplyascript. (MATLAB function ﬁles also have the extension .m. MATLAB therefore

refers to both script and function ﬁles generally as M-ﬁles.) The special signiﬁcance of a script ﬁle is

that, if you enter its name at the command-line prompt, MATLAB carries out each statement in the script

ﬁle as if it were entered at the prompt.

The rules for script ﬁle names are the same as those for MATLAB variable names (see below in

Section 2.3).

As an example, save the compound interest program above in a script ﬁle under the name compint.m.

Then simply enter the name

compint

at the prompt in the Command Window. The statements in compint.m will be carried out exactly

as if you had pasted them into the Command Window. You have effectively created a new MATLAB

command, viz. compint.

A script ﬁle may be listed in the Command Window with the command type,e.g.

type compint

(the extension .m may be omitted).

Script ﬁles provide a useful way of managing large programs which you do not necessarily want to

paste into the Command Window every time you run them.

Current directory

When you run a script, you have to make sure that MATLAB’s current directory (indicated in the Current

Directory ﬁeld on the right of the desktop toolbar) is set to the directory in which the script is saved. To

change the current directory type the path for the new current directory in the Current Directory ﬁeld,

or select a directory from the drop-down list of previous working directories, or click on the browse

button (...) to select a new directory.

14 Essential MATLAB for Scientists and Engineers

The current directory may also be changed in this way from the Current Directory browser in the

desktop.

You can change the current directory from the command line with cd command, e.g.

cd \mystuff

The command cd by itself returns the name of the current directory.

Recommended way to run a script: from the Current Directory browser

A handy way to run a script is as follows. Select the ﬁle in the Current Directory browser. Right-click

it. The context menu appears (context menus are a general feature of the desktop). Select Run from the

context menu. The results appear in the Command Window. If you want to edit the script, select Open

from the context menu.

To specify the types of ﬁles shown in the Current Directory Browser, use View -> Current Directory

Filter. For example, you may wish to see only M-ﬁles. Alternatively, you can right-click the column

title in the Current Directory browser and use the context menu.

You can sort the ﬁles in the Current Directory browser by clicking the title of the ﬁle column. A click

‘toggles’ the sort, i.e. from ascending to descending order or vice versa.

Note that the Help portion of an M-ﬁle appears in the pane at the bottom of the Current Directory

browser. Try this out some M-ﬁles in one of the MATLAB directories, e.g. \toolbox\matlab\elmat.

A one-line description of the M-ﬁle appears in the right-most column of the Current Directory browser

(you may need to enlarge the browser to see all the columns).

How a program works

We will now discuss in detail how the compound interest program works.

The MATLAB system is technically called an interpreter (as opposed to a compiler ). This means

that each statement presented to the command line is translated (interpreted) into language the computer

understands better, and then immediately carried out.

A fundamental concept in MATLAB is how numbers are stored in the computer’s random access

memory (RAM). If a MATLAB statement needs to store a number, space in the RAM is set aside for it.

You can think of this part of the memory as a bank of boxes or memory locations, each of which can

hold only one number at a time. These memory locations are referred to by symbolic names in MATLAB

statements. So the statement

balance = 1000

allocates the number 1000 to the memory location named balance. Since the contents of balance

may be changed during a session it is called a variable.

The statements in our program are therefore interpreted by MATLAB as follows:

1. Put the number 1000 into variable balance.

2. Put the number 0.09 into variable rate.

3. Multiply the contents of rate by the contents of balance and put the answer in interest.

4. Add the contents of balance to the contents of interest and put the answer in balance.

5. Display (in the Command Window) the message given in single quotes.

6. Display the contents of balance.

In hardly seems necessary to stress this, but these interpreted statements are carried out in order from

the top down. When the program has ﬁnished running, the variables used will have the following values:

balance : 1090

interest : 90

rate : 0.09

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