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POHow should I format my .dat file so that a 3D vector plot can be made?
 

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  1. POHow should I format my .dat file so that a 3D vector plot can be made?
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    <p>I'm working this programming task for college where we have to write a <code>c++</code> program that calculates the magnetic field vector for certain coils in 3D space. </p> <p>I've managed to write this program and I think I've got it working pretty well. </p> <p>I want to add in a special thinh though (it's my exam paper, so it has to be extra good!): I wan't to plot the vectors out.</p> <p>I'm used to calling <code>gnuplot</code> from <code>c++</code> (via piping) and this is what I usually do:</p> <ol> <li>create an output stream that writes the data to a <code>.dat</code> file</li> <li>open a gnuplot pipe</li> <li>make gnuplot plot all the contents of the <code>.dat</code></li> </ol> <p>Since my data has always been 2D, <code>x</code>and <code>y</code> plots, I'm quite lost here. My question is:</p> <ol> <li>How to format the <code>.dat</code> file (e.g. do I use braces to group vector components?)</li> <li>what is the actual gnuplot command to plot a 3D vector field?</li> </ol> <p>It'd be easy if I could format the <code>.dat</code> file like this:</p> <pre><code># Px Py Pz Bx By Bz 1 0 2 0.7 0.5 0.25 #&lt;= example data line ... more data ... </code></pre> <p>when the magnetic field vector in the point <code>P=(1,0,2)</code>equals a vector <code>B=(0.7,0.5,0.25)</code>. This would be easy to program, the real question is: will this do ? and how to I plot it in gnuplot. (wow, I've asked the same question 3 times I guess).</p> <hr> <h2><em>Piping</em> to gnuplot</h2> <p>Ok, since someone asked me to describe how I <em>pipe</em> (don't know if it's the right term thought) stuff to <code>gnuplot</code>. Here it is:</p> <ol> <li><p>First open up a pipe and call it <code>pipe</code>:</p> <pre><code>FILE *pipe = popen("gnuplot -persist 2&gt;/dev/null", "w"); </code></pre></li> <li><p>Tell <code>gnuplot</code> what to do through the pipe:</p> <pre><code>fprintf(pipe, "set term x11 enhanced \n"); fprintf(pipe, "plot x^2 ti 'x^2' with lines\n"); </code></pre> <p>notice the <code>\n</code>which is absolutely necessary. It is what executes the command.</p></li> <li><p>close the pipe:</p> <pre><code>pclose(pipe); </code></pre></li> </ol> <p>The necessary library is called <code>&lt;fstream&gt;</code> I believe. </p>
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    1. COI'm very interested in the "pipe" way you use to call gnuplot in 2D. Can you give a brief piece of code? Thanks!
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