Using Octave
First, follow the installation guide
to install GNU Octave on your system. Then, launch the interactive prompt by
typing octave in a terminal or by clicking the icon in the programs menu.
For further guidance, see the manual page on
Running Octave.
Variable Assignment
Assign values to variables with = (Note: assignment is pass-by-value).
Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Variables.html">about variables</a>.
a = 1;
Comments
# or % start a comment line, that continues to the end of the line.
Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Comments.html">about comments</a>.
Command evaluation
The output of every command is printed to the console unless terminated with
a semicolon ;. The <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFdisp.html">disp</a> command can be used to print output
anywhere. Use <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFquit.html">exit</a> or <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFquit.html">quit</a> to quit the console.
Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Simple-Examples.html">about command evaluation</a>.
t = 99 + 1 <span class="comment"># prints 't = 100'</span> t = 99 + 1; <span class="comment"># nothing is printed</span> disp(t);
t = 100100
Elementary math
Many mathematical operators are available in addition to the standard arithmetic. Operations are floating-point. Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Arithmetic.html">about elementary math</a>.
x = 3/4*pi; y = sin(x)
y = 0.70711
Matrices
Arrays in Octave are called matrices. One-dimensional matrices are referred
to as vectors. Use a space or a comma , to separate elements in a row and
semicolon ; to start a new row. Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Linear-Algebra.html">about matrices</a>.
rowVec = [8 6 4]
rowVec =8 6 4
columnVec = [8; 6; 4]
columnVec =8 6 4
mat = [8 6 4; 2 0 -2]
mat =8 6 4 2 0 -2
size(mat)
ans =2 3
length(rowVec)
ans = 3
Linear Algebra
Many common linear algebra operations are simple to program using Octave’s matrix syntax. Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Linear-Algebra.html">about linear algebra</a>.
columnVec * rowVec
ans =64 48 32 48 36 24 32 24 16
rowVec * columnVec
ans = 116
columnVec<span class="string">'</span>
ans =8 6 4
Accessing Elements
Octave is 1-indexed. Matrix elements are accessed as
matrix(rowNum, columnNum). Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Index-Expressions.html">about accessing elements</a>.
mat(2,3)
ans = -2
Control flow wih loops
Octave supports for and while loops, as well as other control flow
structures. Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Statements.html">about control flow</a>.
x = zeros (50,1); <span class="keyword">for</span> i = 1:2:100 <span class="comment"># iterate from 1 to 100 with step size 2</span> x(i) = i^2; <span class="keyword">endfor</span> y = zeros (50,1); k = 1; step = 2; <span class="keyword">while</span> (k <= (100-step)) y(i) = k^2; k = k + step; <span class="keyword">endwhile</span>
Vectorization
For-loops can often be replaced or simplified using vector syntax. The
operators *, /, and ^ all support element-wise operations writing
a dot . before the operators. Many other functions operate element-wise
by default (<a href="https://www.gnu.org/software/octave/doc/interpreter/XREFsin.html">sin</a>, +, -, etc.). Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Vectorization-and-Faster-Code-Execution.html">about vectorization</a>.
i = 1:2:100; <span class="comment"># create an array with 50-elements</span> x = i.^2; <span class="comment"># each element is squared</span> y = x + 9; <span class="comment"># add 9 to each element</span> z = y./i; <span class="comment"># divide each element in y by the corresponding value in i</span> w = sin (i / 10); <span class="comment"># take the sine of each element divided by 10</span>
Plotting
The function <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFplot.html">plot</a> can be called with vector arguments to create 2D line and scatter plots. Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Two_002dDimensional-Plots.html">about plotting</a>.
plot (i/10, w); title (<span class="string">'w = sin(i/10)'</span>); xlabel (<span class="string">'i ÷ 10'</span>); ylabel (<span class="string">'w'</span>);
<img src="octave_basics-1.png" alt="octave_basics-1.png">
Strings
Strings are simply arrays of characters. Strings can be composed using C-style formatting with <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFsprintf.html">sprintf</a> or <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFfprintf.html">fprintf</a>. Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Strings.html">about strings</a>.
firstString = <span class="string">"hello world"</span>; secondString = <span class="string">"!"</span>; [firstString, secondString] <span class="comment"># concatenate both strings</span>
ans = hello world!
fprintf (<span class="string">"%s %.10f \n"</span>, <span class="string">"The number is:"</span>, 10)
The number is: 10.0000000000
If-else
Conditional statements can be used to create branching logic in your code. Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/The-if-Statement.html">in the manual</a>.
<span class="comment"># Print 'Foo' if divisible by 7,</span>
<span class="comment"># 'Fizz' if divisible by 3,</span>
<span class="comment"># 'Buzz' if divisible by 5,</span>
<span class="comment"># 'FizzBuzz' if divisible by 3 and 5</span>
<span class="keyword">for</span> i = 1:1:20
outputString = <span class="string">""</span>;
<span class="keyword">if</span> (rem (i, 3) == 0) <span class="comment"># rem is the remainder function</span>
outputString = [outputString, <span class="string">"Fizz"</span>];
<span class="keyword">endif</span>
<span class="keyword">if</span> (rem (i, 5) == 0)
outputString = [outputString, <span class="string">"Buzz"</span>];
<span class="keyword">elseif</span> (rem(i,7) == 0)
outputString = <span class="string">"Foo"</span>;
<span class="keyword">else</span>
outputString = outputString;
<span class="keyword">endif</span>
fprintf(<span class="string">"i=%g: %s \n"</span>, i, outputString);
<span class="keyword">endfor</span>i=1:i=2: i=3: Fizz i=4: i=5: Buzz i=6: Fizz i=7: Foo i=8: i=9: Fizz i=10: Buzz i=11: i=12: Fizz i=13: i=14: Foo i=15: FizzBuzz i=16: i=17: i=18: Fizz i=19: i=20: Buzz
Getting Help
The <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFhelp.html">help</a> and <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFdoc.html">doc</a> commands can be invoked at the
Octave prompt to print documentation for any function.
help plot doc plot
Octave forge packages
Community-developed packages can be added from the <a href="http://octave.sourceforge.net/index.html">Octave Forge</a> website to extend the functionality of Octave’s core library. (Matlab users: Forge packages act similarly to Matlab’s toolboxes.) The <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFpkg.html">pkg</a> command is used to manage these packages. For example, to use the image processing library
from the Forge, use:
pkg install -forge image <span class="comment"># install package</span> pkg load image <span class="comment"># load new functions into workspace</span>
<a href="https://www.gnu.org/software/octave/doc/interpreter/Packages.html">Read more about packages</a>.