# Get started with Octave

## Download and install Octave

There are a number of Open Source alternatives to the program MatLab, one of the most known alternatives is GNU Octave. When using Octave you use a command line to enter commands. Octave can be downloaded and installed from GNU Octave.

### Install on Mac

If using Mac:

Install Homebrew.

Install XCode from App Store.

Open and run the XCode app to agree to the License Agreement.

Install XQuartz.

Import science packages, open the terminal and enter:

brew tap homebrew/science

Install Octave (this takes time):

brew update && brew upgrade brew install gcc brew install octave --without-docs

Update:

brew update && brew upgrade

At the end of the process a summary is shown displaying the path to Octave. If following is shown:

Summary /usr/local/Cellar/octave/3.8.1

then the path to Octave is `/usr/local/Cellar/octave/3.8.1/bin/Octave`

Open AppleScript Editor and make a New Document. Write following:

tell application "Terminal" do script "/path/to/octave; exit" end tell

where `/path/to/octave`

is the path. Save the script as Octave.app, select Application when saving.

For more information see Octave for MacOS X.

## As a calculator

The easiest way to get started, is to use Octave as a calculator.

The arithmetic operators are:

`+ - * / ^`

(to the power of) There are predefined constants in Octave, some of them are listed below:

constant | explanation |
---|---|

`pi ` , `e ` , `i` |
Make a wild guess! |

`Inf` (infinity) |
Operations yielding numbers larger than the maximum floating point will give this answer. |

`NaN` (not a number) |
Operations that can not be defined in any reasonably way will give this answer |

There are also a number of predefined mathematical functions in Octave, some of them are listed below:

function | explanation |
---|---|

`sin, cos, tan` |
Trigonometric functions using radians |

`asin, acos, atan` |
Inverse trigonometric functions |

`exp, log, log10` |
Exponential function, natural logarithm, logarithm to the base 10 |

`sqrt` |
Square root |

`abs` |
Absolute value |

`round, floor, ceil` |
Round to nearest integer, round down, round up |

`rem` |
Remainder when doing integer division |

### Showing more decimals

You can show more decimals by typing `format long`

. Go back to showing
few decimals by typing `format short`

.

## Exercise 1

Calculate following expressions

- \(\sqrt[5]{200}\)
- \(\dfrac{3\cdot 10^{-3}}{0.001+\sqrt{0.2}}\)

- \(\dfrac{2^{3+\sin{0.3}}+5}{10}\)

You should get these answers

`ans = 2.8854`

`ans = 0.0066932`

`ans = 1.4819`

You can see old commands by using up/down arrow keys.

## Exercise 2

Guess the output of following commands, then check the answers given by Octave

`1/0 0/0 tan(pi/2)`

`inf+inf inf-inf inf/inf inf*inf`

`nan+2 nan+nan`

## Exit Octave

Exit Octave by writing `exit`

or `quit`

.

by Malin Christersson under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 Sweden License