Using Octave: Difference between revisions

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The output of every command is printed to the console unless terminated with
The output of every command is printed to the console unless terminated with
a semicolon <code>;</code>.  The <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFdisp.html">disp</a> command can be used to print output
a semicolon <code>;</code>.  The [https://www.gnu.org/software/octave/doc/interpreter/XREFdisp.html disp] 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.
anywhere.  Use [https://www.gnu.org/software/octave/doc/interpreter/XREFquit.html exit] or [https://www.gnu.org/software/octave/doc/interpreter/XREFquit.html quit] to quit the console.
Read more
Read more [https://www.gnu.org/software/octave/doc/interpreter/Simple-Examples.html about command evaluation].
<a href="https://www.gnu.org/software/octave/doc/interpreter/Simple-Examples.html">about command evaluation</a>.</p><pre class="oct-code">t = 99 + 1  <span class="comment"># prints 't = 100'</span>
t = 99 + 1; <span class="comment"># nothing is printed</span>
disp(t);</pre><pre class="oct-code-output">t =  100
100
</pre>


<syntaxhighlight lang="octave">t = 99 + 1  # prints 't = 100'</syntaxhighlight>
<syntaxhighlight lang="text">t =  100</syntaxhighlight>


<syntaxhighlight lang="octave">t = 99 + 1; # nothing is printed
disp(t);</syntaxhighlight>
<syntaxhighlight lang="text"> 100</syntaxhighlight>


= Elementary math =
= Elementary math =
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Many mathematical operators are available in addition to the standard
Many mathematical operators are available in addition to the standard
arithmetic.  Operations are floating-point.  Read more
arithmetic.  Operations are floating-point.  Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Arithmetic.html">about elementary math</a>.</p><pre class="oct-code">x = 3/4*pi;
[https://www.gnu.org/software/octave/doc/interpreter/Arithmetic.html about elementary math].
y = sin(x)</pre><pre class="oct-code-output">y =  0.70711
 
</pre>
<syntaxhighlight lang="octave">x = 3/4 * pi;
y = sin (x)</syntaxhighlight>
<syntaxhighlight lang="text">y =  0.70711</syntaxhighlight>
 




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to as vectors.  Use a space or a comma <code>,</code> to separate elements in a row and
to as vectors.  Use a space or a comma <code>,</code> to separate elements in a row and
semicolon <code>;</code> to start a new row.  Read more
semicolon <code>;</code> to start a new row.  Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Linear-Algebra.html">about matrices</a>.</p><pre class="oct-code">rowVec = [8 6 4]</pre><pre class="oct-code-output">rowVec =
[https://www.gnu.org/software/octave/doc/interpreter/Linear-Algebra.html about matrices].
<syntaxhighlight lang="octave">rowVec = [8 6 4]</syntaxhighlight>
<syntaxhighlight lang="text">rowVec =
   8  6  4
   8  6  4
</pre><pre class="oct-code">columnVec = [8; 6; 4]</pre><pre class="oct-code-output">columnVec =
</syntaxhighlight>
 
<syntaxhighlight lang="octave">columnVec = [8; 6; 4]</syntaxhighlight>
<syntaxhighlight lang="text">columnVec =
   8
   8
   6
   6
   4
   4
</pre><pre class="oct-code">mat = [8 6 4; 2 0 -2]</pre><pre class="oct-code-output">mat =
</syntaxhighlight>
 
<syntaxhighlight lang="octave">mat = [8 6 4; 2 0 -2]</syntaxhighlight>
<syntaxhighlight lang="text">mat =
   8  6  4
   8  6  4
   2  0  -2
   2  0  -2
</pre><pre class="oct-code">size(mat)</pre><pre class="oct-code-output">ans =
</syntaxhighlight>
 
<syntaxhighlight lang="octave">size(mat)</syntaxhighlight>
<syntaxhighlight lang="text">ans =
   2  3
   2  3
</pre><pre class="oct-code">length(rowVec)</pre><pre class="oct-code-output">ans =  3
</syntaxhighlight>
</pre>
 
<syntaxhighlight lang="octave">length(rowVec)</syntaxhighlight>
<syntaxhighlight lang="text">ans =  3</syntaxhighlight>




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Many common linear algebra operations are simple to program using Octave’s
Many common linear algebra operations are simple to program using Octave’s
matrix syntax.  Read more
matrix syntax.  Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Linear-Algebra.html">about linear algebra</a>.</p><pre class="oct-code">columnVec * rowVec</pre><pre class="oct-code-output">ans =
[https://www.gnu.org/software/octave/doc/interpreter/Linear-Algebra.html about linear algebra].
 
<syntaxhighlight lang="octave">columnVec * rowVec</syntaxhighlight>
<syntaxhighlight lang="text">ans =
   64  48  32
   64  48  32
   48  36  24
   48  36  24
   32  24  16
   32  24  16
</pre><pre class="oct-code">rowVec * columnVec</pre><pre class="oct-code-output">ans =  116
</syntaxhighlight>
</pre><pre class="oct-code">columnVec<span class="string">'</span></pre><pre class="oct-code-output">ans =
  8  6  4
</pre>


<syntaxhighlight lang="octave">rowVec * columnVec</syntaxhighlight>
<syntaxhighlight lang="text">ans =  116</syntaxhighlight>


<syntaxhighlight lang="octave">columnVec'</syntaxhighlight>
<syntaxhighlight lang="text">ans =
  8  6  4
</syntaxhighlight>


= Accessing Elements =
= Accessing Elements =
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Octave is 1-indexed.  Matrix elements are accessed as
Octave is 1-indexed.  Matrix elements are accessed as
<code>matrix(rowNum, columnNum)</code>.  Read more
<code>matrix(rowNum, columnNum)</code>.  Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Index-Expressions.html">about accessing elements</a>.</p><pre class="oct-code">mat(2,3)</pre><pre class="oct-code-output">ans = -2
[https://www.gnu.org/software/octave/doc/interpreter/Index-Expressions.html about accessing elements].
</pre>


<syntaxhighlight lang="octave">mat(2,3)</syntaxhighlight>
<syntaxhighlight lang="text">ans = -2</syntaxhighlight>




= Control flow wih loops =
 
= Control flow with loops =


Octave supports <code>for</code> and <code>while</code> loops, as well as other control flow
Octave supports <code>for</code> and <code>while</code> loops, as well as other control flow
structures.  Read more
structures.  Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Statements.html">about control flow</a>.</p><pre class="oct-code">x = zeros (50,1);
[https://www.gnu.org/software/octave/doc/interpreter/Statements.html about control flow].
<span class="keyword">for</span> i = 1:2:100 <span class="comment"># iterate from 1 to 100 with step size 2</span>
 
<syntaxhighlight lang="octave">x = zeros (50,1);
for i = 1:2:100 # iterate from 1 to 100 with step size 2
   x(i) = i^2;
   x(i) = i^2;
<span class="keyword">endfor</span>
endfor


y = zeros (50,1);
y = zeros (50,1);
k = 1;
k = 1;
step = 2;
step = 2;
<span class="keyword">while</span> (k <= (100-step))
while (k <= 100)
   y(i) = k^2;
   y(k) = k^2;
   k = k + step;
   k = k + step;
<span class="keyword">endwhile</span></pre><pre class="oct-code-output"></pre>
endwhile</syntaxhighlight>
 
 


= Vectorization =
= Vectorization =
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operators <code>*</code>, <code>/</code>, and <code>^</code> all support element-wise operations writing
operators <code>*</code>, <code>/</code>, and <code>^</code> all support element-wise operations writing
a dot <code>.</code> before the operators.  Many other functions operate element-wise
a dot <code>.</code> 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>, <code>+</code>, <code>-</code>, etc.).  Read more
by default ([https://www.gnu.org/software/octave/doc/interpreter/XREFsin.html sin], <code>+</code>, <code>-</code>, etc.).  Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Vectorization-and-Faster-Code-Execution.html">about vectorization</a>.</p><pre class="oct-code">i = 1:2:100;      <span class="comment"># create an array with 50-elements</span>
[https://www.gnu.org/software/octave/doc/interpreter/Vectorization-and-Faster-Code-Execution.html about vectorization].
x = i.^2;        <span class="comment"># each element is squared</span>
 
y = x + 9;        <span class="comment"># add 9 to each element</span>
<syntaxhighlight lang="octave">i = 1:2:100;      # create an array with 50-elements
z = y./i;        <span class="comment"># divide each element in y by the corresponding value in i</span>
x = i.^2;        # each element is squared
w = sin (i / 10); <span class="comment"># take the sine of each element divided by 10</span>
y = x + 9;        # add 9 to each element
</pre><pre class="oct-code-output"></pre>
z = y./i;        # divide each element in y by the corresponding value in i
w = sin (i / 10); # take the sine of each element divided by 10
</syntaxhighlight>




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= Plotting =
= Plotting =


The function <a href="https://www.gnu.org/software/octave/doc/interpreter/XREFplot.html">plot</a> can be called with vector arguments to
The function [https://www.gnu.org/software/octave/doc/interpreter/XREFplot.html plot] can be called with vector arguments to
create 2D line and scatter plots.  Read more
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>.</p><pre class="oct-code">plot (i/10, w);
[https://www.gnu.org/software/octave/doc/interpreter/Two_002dDimensional-Plots.html about plotting].
title (<span class="string">'w = sin(i/10)'</span>);
xlabel (<span class="string">'i ÷ 10'</span>);
ylabel (<span class="string">'w'</span>);</pre><pre class="oct-code-output"></pre><img src="octave_basics-1.png" alt="octave_basics-1.png">


<syntaxhighlight lang="octave">plot (i / 10, w);
title ('w = sin (i / 10)');
xlabel ('i / 10');
ylabel ('w');</syntaxhighlight>


[[File:Using octave-1.png|thumb|center]]


= Strings =
= Strings =


Strings are simply arrays of characters.  Strings can be composed using
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
C-style formatting with [https://www.gnu.org/software/octave/doc/interpreter/XREFsprintf.html sprintf] or
<a href="https://www.gnu.org/software/octave/doc/interpreter/XREFfprintf.html">fprintf</a>.  Read more
[https://www.gnu.org/software/octave/doc/interpreter/XREFfprintf.html fprintf].  Read more
<a href="https://www.gnu.org/software/octave/doc/interpreter/Strings.html">about strings</a>.</p><pre class="oct-code">firstString = <span class="string">"hello world"</span>;
[https://www.gnu.org/software/octave/doc/interpreter/Strings.html about strings].
secondString = <span class="string">"!"</span>;
 
[firstString, secondString] <span class="comment"># concatenate both strings</span>
<syntaxhighlight lang="octave">firstString = "hello world";
</pre><pre class="oct-code-output">ans = hello world!
secondString = "!";
</pre><pre class="oct-code">fprintf (<span class="string">"%s %.10f \n"</span>, <span class="string">"The number is:"</span>, 10)</pre><pre class="oct-code-output">The number is: 10.0000000000  
[firstString, secondString] # concatenate both strings
</pre>
</syntaxhighlight>
<syntaxhighlight lang="text">ans = hello world!</syntaxhighlight>
 
<syntaxhighlight lang="octave">fprintf ("%s %.10f \n", "The number is:", 10)</syntaxhighlight>
<syntaxhighlight lang="text">The number is: 10.0000000000</syntaxhighlight>




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Conditional statements can be used to create branching logic in your code.
Conditional statements can be used to create branching logic in your code.
Read more
Read more [https://www.gnu.org/software/octave/doc/interpreter/The-if-Statement.html in the manual].
<a href="https://www.gnu.org/software/octave/doc/interpreter/The-if-Statement.html">in the manual</a>.</p><pre class="oct-code"><span class="comment"># Print 'Foo'      if divisible by 7,</span>
 
<span class="comment">#      'Fizz'    if divisible by 3,</span>
<syntaxhighlight lang="octave"># Print 'Foo'      if divisible by 7,
<span class="comment">#      'Buzz'    if divisible by 5,</span>
#      'Fizz'    if divisible by 3,
<span class="comment">#      'FizzBuzz' if divisible by 3 and 5</span>
#      'Buzz'    if divisible by 5,
<span class="keyword">for</span> i = 1:1:20
#      'FizzBuzz' if divisible by 3 and 5
   outputString = <span class="string">""</span>;
for i = 1:1:20
   <span class="keyword">if</span> (rem (i, 3) == 0)  <span class="comment"># rem is the remainder function</span>
   outputString = "";
     outputString = [outputString, <span class="string">"Fizz"</span>];
   if (rem (i, 3) == 0)  # rem is the remainder function
   <span class="keyword">endif</span>
     outputString = [outputString, "Fizz"];
   <span class="keyword">if</span> (rem (i, 5) == 0)
   endif
     outputString = [outputString, <span class="string">"Buzz"</span>];
   if (rem (i, 5) == 0)
   <span class="keyword">elseif</span> (rem(i,7) == 0)
     outputString = [outputString, "Buzz"];
     outputString = <span class="string">"Foo"</span>;
   elseif (rem(i,7) == 0)
   <span class="keyword">else</span>
     outputString = "Foo";
   else
     outputString = outputString;
     outputString = outputString;
   <span class="keyword">endif</span>
   endif
   fprintf(<span class="string">"i=%g: %s \n"</span>, i, outputString);
   fprintf("i=%g: %s \n", i, outputString);
<span class="keyword">endfor</span></pre><pre class="oct-code-output">i=1:   
endfor</syntaxhighlight>
 
<syntaxhighlight lang="text">i=1:   
i=2:   
i=2:   
i=3: Fizz  
i=3: Fizz  
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i=19:   
i=19:   
i=20: Buzz  
i=20: Buzz  
</pre>
</syntaxhighlight>




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= Getting Help =
= 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
The [https://www.gnu.org/software/octave/doc/interpreter/XREFhelp.html help] and [https://www.gnu.org/software/octave/doc/interpreter/XREFdoc.html doc] commands can be invoked at the
Octave prompt to print documentation for any function.</p><pre class="pre-code">help plot
Octave prompt to print documentation for any function.
doc plot</pre>
 
<syntaxhighlight lang="octave">help plot
doc plot</syntaxhighlight>




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Community-developed packages can be added from the
Community-developed packages can be added from the
<a href="http://octave.sourceforge.net/index.html">Octave Forge</a> website to extend
[http://octave.sourceforge.net/index.html Octave Forge] website to extend
the functionality of Octave’s core library.  (Matlab users: Forge packages
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
act similarly to Matlab’s toolboxes.)  The [https://www.gnu.org/software/octave/doc/interpreter/XREFpkg.html pkg] command is used
to manage these packages.  For example, to use the image processing library
to manage these packages.  For example, to use the image processing library
from the Forge, use:</p><pre class="pre-code">pkg install -forge image <span class="comment"># install package</span>
from the Forge, use:
pkg load image          <span class="comment"># load new functions into workspace</span>
 
</pre><p><a href="https://www.gnu.org/software/octave/doc/interpreter/Packages.html">Read more about packages</a>.</p>
<syntaxhighlight lang="octave">pkg install -forge image # install package
pkg load image          # load new functions into workspace
</syntaxhighlight>
 
[https://www.gnu.org/software/octave/doc/interpreter/Packages.html Read more about packages].


[[Category:Tutorials]]
[[Category:Tutorials]]
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