伯尔尼应用科学大学Andreas Stahel教授的Octave编程入门与工程应用教程

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Octave编程指南是由瑞士伯尔尼应用科学大学的Andreas Stahel教授编写的，这是一本面向工程问题解决的教程。Octave被设计为一种高度可读的、解释型的编程语言，其语法与MATLAB非常相似，这使得MATLAB用户能够轻松地迁移至Octave环境。该书的核心目标是帮助学生熟悉Octave的基本用法和数据结构，通过提供实例来展示常用命令的使用，以及强调在两种语言之间的差异。第一章作为入门，着重于基础概念，涵盖了Octave的基本命令集和数据类型，例如矩阵操作、变量定义、函数创建等。通过一系列简单易懂的示例，读者可以快速掌握如何在实际项目中运用这些功能。同时，作者还特别注重比较Octave与MATLAB在功能和执行效率上的异同，以帮助学习者理解并选择最适合他们需求的工具。第二章则深入到实际应用层面，每个部分围绕一个特定的问题或任务展开，利用Octave进行求解。这些应用涵盖广泛的领域，如图像处理、数学建模、控制系统设计等，旨在让读者能够将所学知识运用到实际工程问题中。每个问题的解决方案都提供了对Octave功能的实战演示，帮助读者增强解决问题的能力。此外，书中还包含了许多可供下载的代码示例，读者可以在web.ti.bfh.ch/˜sha1/Labs/PWF/Codes找到它们，以便在实践中进一步加深对Octave的理解。总体而言，这本书不仅适合Octave初学者，也是现有MATLAB用户的过渡教材，对于提升工程问题解决能力具有很高的实用价值。

1.1. STARTING UP OCTAVE OR MATLAB AND FIRST STEPS 15

optim | 1 .5 . 2 | / home/ sha1 / o ctave / forge / optim −1.5.2

s i g n a l | 1 .3 . 2 | / home/ sha1 / octave / forge / sig n a l −1.3.2

s pl i n e s | 1 .3 . 2 | / home/ sha1 / o ctave / forge / sp l ine s −1.3.2

s t a t i s t i c s | 1 . 3. 0 | / home / sha1 / oct ave / fo r g e / s t a t i s t i c s −1.3.0

s t r u c t | 1. 0 . 14 | / home / sha1 / octave / fo r g e / s t r u c t −1.0.14

• With the commands ispc(), isunix() and ismac() you can ﬁnd out what operating system is

currently used. These commands are useful for code depending on the OS, e.g. the exact form of ﬁle

and directory names.

Octave

[ ispc ( ) , i s un i x ( ) , ismac ( ) ]

−−> 0 1 0

The results shows that currenly a Unix system is running, in this case Linux. With

Octave

oct ave :16> i s i e e e ( )

−−> 1

verify that your system conforms to the IEEE standard for ﬂoating point calculations.

• With the command getrusage() you can extract information about the current Octave process,

e.g. memory usage and CPU usage.

1.1.4 Starting up MATLAB

A working environment for MATLAB consists of

1. a command line shell with MATLAB to launch the commands

2. an editor to write the code

3. possibly a browser to access the documentation

4. possilbly one or more graphics windows

To start up MATLAB on a Unix system at our school you may proceed as follows:

• Open a shell or terminal

• Change to the directory in which you want to work, use cd .

• If you type matlab & then MATLAB will launch with the ﬂashy Java interface. Using the ampersand

& allows you to launch other commands in the same shell. Do not combine the option -nojvm and

MATLAB as a background process, since you need the shell for input and output when no Java inteface

is started.

• Type matlab -nojvm & to launch MATLAB. The option -nojvm launches MATLAB without the

splashy Java interface and thus uses a lot less memory, which might be precious resource your system.

On newer versions of MATLAB some of the features are not available without the Java interface, this

concerns mainly the handling of graphics.

• You may also use the GUI of your operating system, locate the menu entry for MATLAB click on it

and the program will start.

– After a short wait a ﬂashy interface should appear on the screen.

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1.1. STARTING UP OCTAVE OR MATLAB AND FIRST STEPS 16

– On the right you ﬁnd the command line for MATLAB. Elementary commands may be entered on

this line.

– On the left you ﬁnd a history of the previously applied commands

– On the top you can choose the working directory and a few menus

– When you launch MATLAB with the interface you will use considerably more memory for the

interface (Java) and Greek characters will not show on the screen. You will have to set the

working directory with a cd command.

• When typing the command edit an elementary editor will show up. It might be useful to type longer

codes and store them in a regular text ﬁle with the extension .m , the standard for any MATLAB ﬁle.

You are free to use your favorite editor to work on your codes.

• On startup MATLAB will read a ﬁle startup.m in a subdirectory matlab of the users home

directory. Often it is in ˜/Documents/MATLAB/ . In this ﬁle the user can give commands to

MATLAB to be applied at each startup.

1.1.5 Calling the operating system and using basic Unix commands

Within Octave or MATLAB it is possible to launch programs of the operating system. This can be very

useful, e.g. to call external image processing tools, see page 85. The details for the functions obviously

depend on the underlying operating system.

• system() : execute a shell command and return the status and result of the command. As a simple

example call the command whoami which returns the current users name.

unix ( ’whoami ’ ) ;

−−>

sha1

• unix() : execute a system command if running under a Unix-like operating system, otherwise do

nothing.

• dos() : execute a system command if running under a Dos or Windows-like operating system,

otherwise do nothing.

With MATLAB the three commands system(), unix() and dos() are interchangeable. With Octave

their result depends on the operating system. It is a good idea to use the command system() only.

When working on a computer system some basic commands might be handy. Table 1.1 shows a few

useful Unix commands. Some of the commands also work on the Octave/MATLAB command line. The

behavior on a Win* system might be different.

1.1.6 How to ﬁnd out whether you are working with MATLAB or Octave

There are still very few occasions when the codes for Octave or MATLAB differ slightly. Thus it might

be useful to have a command telling you whether you work with Octave or MATLAB. The command

IsOctave() returns 1 if Octave is running and 0 otherwise. Copy the ﬁle below in directories where

MATLAB/Octave will ﬁnd it, e.g. ˜/Documents/Matlab and ˜/octave/site/ .

isOctave.m

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1.1. STARTING UP OCTAVE OR MATLAB AND FIRST STEPS 17

Unix Octave

show current directory pwd pwd

change into directory MyDir cd MyDir cd MyDir

change one directory level up cd .. cd ..

list all ﬁles in current directory ls ls

list more information about ﬁles ls -al ls -al

remove the ﬁle go.m rm go.m delete go.m

create a directory NewDir mkdir NewDir mkdir NewDir

remove the directory NewDir rmdir NewDir rmdir NewDir

Table 1.1: Basic system commands

f u n cti o n r e s u l t = IsOc tave ( )

% Returns t r u e i f t h i s code i s being executed by Octave .

% Returns f a l s e i f t h i s code i s being exe cuted by MATLAB, or any ot h e r MATLAB

% v a ri an t .

% usage : r e s u l t = is Octave ( )

p e r s i s t e n t o c ta v eVe r si o nIs B ui l tIn ;

i f ( isempty ( o c tav e Ver s io n IsB u il t In ) )

o c tav e Ver s io n IsB u il t In = ( e x i s t ( ’OCTAVE VERSION’ , ’ b u il t i n ’ ) == 5 );

% e x i s t re t u r n s 5 t o i n d i c a te a b u i l t −in f u nct i on .

end

r e s u l t = o ct a veV e rsi o nI s Bui l tI n ;

% I f OCTAVE VERSION i s a b ui lt −in f u n c t i on , then we must be in Octave .

% Since the r e s u l t cannot change between f u nct i on c a l l s , i t i s cached i n a

% p e r s i s t e n t v ar ia bl e . i sOctav e cannot be a p e r s i s t e n t v ari a ble , because i t

% i s the r et ur n value of the f u n c t i o n , so i ns te a d the p e r s i s t e n t r e s u l t must

% be cached in a s e pa ra t e v a r i a b l e .

end

1.1.7 Where and how to get help

There are different situations when help is useful and important

• You know the command and need to know more details. As an example we use the command

plot().

– Typing help plot will display information about the command help. You will ﬁnd a list of

all possible arguments of this function.

– Typing doc plot will put you in an on-line version of the Octave manual with the documen-

tation on plot(). You can use this as a starting points to browse for similar commands. doc

works with Octave only.

– Typing lookfor plot will search in all of the on-line documentation and display a list of all

the commands. Type help lookfor to ﬁnd out more.

• Some commands have demos and example codes built in. Examine the command quiver(). With

example quiver ﬁnd a listing of working examples.

Octave

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1.1. STARTING UP OCTAVE OR MATLAB AND FIRST STEPS 18

example quiver

−−>

quiver example 1 :

c l f ;

[ x , y ] = meshgrid ( 1 : 2 : 2 0 ) ;

h = quiver ( x , y , s i n (2∗pi ∗x / 10 ) , s i n (2∗pi ∗y / 1 0 ) ) ;

t i t l e ( ’ quiver p l o t ’ )

quiver example 2 :

c l f ;

x = l in s pa c e (0 , 3 , 8 0 );

y = s i n (2∗pi ∗x ) ;

t he t a = 2∗pi ∗x + pi / 2 ;

quiver ( x , y , s in ( t h e ta ) / 1 0 , cos ( t h e t a ) /1 0 , 0 . 4 ) ;

ax i s equ al t i g h t ;

hold on ; p lo t ( x , y , ’ r ’ ) ; hold of f ;

t i t l e ( ’ quiver ( ) with s cale d arrows ’ ) ;

By calling demo quiver the examples will be executed and you can examine code and results.

• Most of the Octave code is given as script ﬁle. You can look at the source. As it is Open Source code

you can copy the ﬁle in your directory and modify the code perform the desired operation. To locate

the source code for the command quiver use which.

Octave

which q uiver

−−> ’ quiver ’ i s a f u nct i on from the f i l e

/ usr / l o c a l / share / octave / 4 . 0 . 0 /m/ p l o t / draw / quiver .m

• If you only know the topic for which you need help, but not the exact command (yet), use the Octave

manual.

– Both are available on the net at http://www.gnu.org/software/octave/ and go to Support. You

can browse in the HTML ﬁles or download the PDF ﬁle.

– Both should be installed on your computer in HTML and PDF form.

∗ Search your local disk for the ﬁle octave.html. It should be a directory and then the ﬁle

index.html is the starting point into the HTML manual.

∗ Search your local disk for the ﬁle octave.pdf with the PDF manual.

– The manual for Octave 4.2.0 is also available on my web site at

web.ti.bfh.ch/˜sha1/Octave.html , as HTML (in compressed form, ﬁrst download, then uncom-

press) and as PDF ﬁle.

• The references given on page 7 might also be useful, and hopefully these notes too.

• For the Octave packages the site http://octave.sourceforge.net/ provides documentation.

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