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Tips and tricks

1,282 bytes added, 04:18, 29 October 2017
Real matrix operations: add "Range"
==Preferences==
Sometimes, Octave defaults are not the best for someone's specific use. To change the defaults, use the following on the {{Path|[[.octaverc]]}} file.
=== Changing default figure size ===
{{Code|change default figure size|<pre>set (0, 'DefaultFigurePosition', [1 get(0, "screensize")(4:-1:3) get(0, "DefaultFigurePosition")(4)]);</pre>}}
The value of {{Codeline|DefaultFigurePosition}} must be a four element vector with the x and y coordinates for the figure, followed by its with width and height. The code above sets the default image to be placed at the top of the monitor, with the width of the monitor and the same height previously set as default. === Changing default font for axes === To display tex characters such as '\alpha' or '\lambda', a TrueType font ("arial" for instance) is better for the gnuplot backend [https://savannah.gnu.org/bugs/?30681]{{Code|change default axes font name|<pre>set (0, "DefaultAxesFontName", "Arial")</pre>}}It can then be necessary to change the font size as well{{Code|change default axes font size|<pre>set(0, 'DefaultAxesFontSize', 10)</pre>}}
<tr><td>element multiplication</td><td><code>A.*B</code></td><td><code>product(A,B) </code></td></tr>
<tr><td>element division</td><td><code>A./B</code></td><td><code>quotient(A,B) </code></td></tr>
<tr><td>transpose*</td><td><code>A.'</code></td><td><code>A.transpose()</code></td></tr>
<tr><td>select element m,n of A**</td><td><code>A(m,n)</code></td><td><code>A(m-1,n-1)</code></td></tr>
<tr><td>select row N of A**</td><td><code>A(N,:)</code></td><td><code>A.row(N-1)</code></td></tr>
<tr><td>number of rows</td><td><code>size(A,1)</code></td><td><code>A.rows()</code></td></tr>
<tr><td>number of columns</td><td><code>size(A,2)</code></td><td><code>A.cols()</code></td></tr>
<tr><td>range</td><td><code>0.1:0.2:0.9</code></td><td><code>Range (0.1, 0.9, 0.2).matrix_value ()</code></td></tr>
</table>
*The MathWorks: Code Vectorization Guide: http://www.mathworks.com/support/tech-notes/1100/1109.html
[[Category:TutorialsTips and tricks]]  ===Changing BLAS=== Many Octave functions are wrappers to optimized numerical libraries, notably BLAS and ATLAS. It is possible to achieve impressive performance gains by simply using a library tuned to your platform. One example is using OpenBLAS to replace the default BLAS implementation ([http://www.stat.cmu.edu/~nmv/2013/07/09/for-faster-r-use-openblas-instead-better-than-atlas-trivial-to-switch-to-on-ubuntu/ further details]). On some Linux distributions, this just takes a few commands. For instance, on Ubuntu, it usually suffices to run  sudo apt-get install libopenblas-base libatlas3gf-base followed by  sudo update-alternatives --config libblas.so.3 and then selecting the openblas option.
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