Octave Programming Tutorial/Struct Arrays

Octave Programming Tutorial

Chapter 1: A Tutorial Introduction

Chapter 2: Basic Octave Concepts

Saving and loading a MAT-file

Octave's Command Prompt

Chapter 3: Data Storage and Manipulation

Data Types and Operations on Point Values

Boolean and Rational

Strings

Portable Functions

Complex Numbers

Arrays and Matrices

What is an array?

Introduction to array operations

Vectors and basic vector operations

Struct Arrays

Cell Arrays

Sparce Matrices

Chapter 4: M File Programming

Scripts

Comments

The Input Function

Control Flow

Loops and Branches

Error Messages

Octave Caveats

Debugging M Files

Chapter 5: Graphics

Basic Graphics Commands

Annotating Plots

Chapter 6: Mathematical Manipulations

Linear Algebra

Simple matrix manipulation

More complicated matrix operations

Differential Equations

Ordinary Differential Equations

Partial Differential Equations

Chapter 7: Examples

Filtering

Controls

A structure in Octave groups different data types called fields in a single object. Fields are accessed by their names.

Declaring a structure

A structure is declared by assigning values to its fields. A period (.) separates the name of the field and the name of the structure:

>> city.name = 'Liege';
>> city.country = 'Belgium';
>> city.longitude = 50.6333;
>> city.latitude = 5.5666;

The fields of a structure and their value can by displayed by simply entering the name of the struct:

>> city
city =
{
  name = Liege
  country = Belgium
  longitude =  50.633
  latitude =  5.5666
}

Manipulating structures

A structure can be copied as any objects:

>> city_copy = city;

In most circumstance, the fields of a structure can be manipulated with the period operator. The value of a field can be overwritten by:

>> city.name = 'Outremeuse';

In the same way, the value of a field can be retrieved by:

>> city.name
ans = Outremeuse

The function isstruct can be used to test if object is a structure or not. With the function fieldnames all field names are returned as a cell array:

>> fieldnames(city)
ans =
{
  [1,1] = name
  [2,1] = country
  [3,1] = longitude
  [4,1] = latitude
}

To test if a structure contains the a given field named, the function isfield can be used:

>> isfield(city,'name')
ans =  1

The value of a field can be extract with getfield:

>> getfield(city,'name')
ans = Liege

In a similar way, the value of a field can be set with setfield:

>> setfield(city,'name','Outremeuse')

The functions isfield, getfield and setfield are useful when the names of a structure are determined during execution of the program.