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<a href="#define-members">Macros</a> &#124;
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<div class="title">spirograph.c File Reference</div> </div>
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<p>Implementation of <a href="https://en.wikipedia.org/wiki/Spirograph">Spirograph</a>
<a href="#details">More...</a></p>
<div class="textblock"><code>#include &lt;math.h&gt;</code><br />
<code>#include &lt;stdbool.h&gt;</code><br />
<code>#include &lt;stdio.h&gt;</code><br />
<code>#include &lt;stdlib.h&gt;</code><br />
<code>#include &lt;time.h&gt;</code><br />
</div><div class="textblock"><div class="dynheader">
Include dependency graph for spirograph.c:</div>
<div class="dyncontent">
<div class="center"><iframe scrolling="no" frameborder="0" src="../../da/dd5/spirograph_8c__incl.svg" width="430" height="112"><p><b>This browser is not able to show SVG: try Firefox, Chrome, Safari, or Opera instead.</b></p></iframe>
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#define&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="../../d7/d98/spirograph_8c.html#a525335710b53cb064ca56b936120431e">_USE_MATH_DEFINES</a></td></tr>
<tr class="memdesc:a525335710b53cb064ca56b936120431e"><td class="mdescLeft">&#160;</td><td class="mdescRight">required for MSVC compiler <br /></td></tr>
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Functions</h2></td></tr>
<tr class="memitem:a0daa148091ec953809fc172289f773d3"><td class="memItemLeft" align="right" valign="top">void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="../../d7/d98/spirograph_8c.html#a0daa148091ec953809fc172289f773d3">spirograph</a> (double *x, double *y, double l, double k, size_t N, double rot)</td></tr>
<tr class="memdesc:a0daa148091ec953809fc172289f773d3"><td class="mdescLeft">&#160;</td><td class="mdescRight">Generate spirograph curve into arrays <code>x</code> and <code>y</code> such that the i^th point in 2D is represented by <code>(x[i],y[i])</code>. <a href="../../d7/d98/spirograph_8c.html#a0daa148091ec953809fc172289f773d3">More...</a><br /></td></tr>
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void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="../../d7/d98/spirograph_8c.html#a708a4c1a4d0c4acc4c447310dd4db27f">test</a> (void)</td></tr>
<tr class="memdesc:a708a4c1a4d0c4acc4c447310dd4db27f"><td class="mdescLeft">&#160;</td><td class="mdescRight">Test function to save resulting points to a CSV file. <br /></td></tr>
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int&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="../../d7/d98/spirograph_8c.html#a3c04138a5bfe5d72780bb7e82a18e627">main</a> (int argc, char **argv)</td></tr>
<tr class="memdesc:a3c04138a5bfe5d72780bb7e82a18e627"><td class="mdescLeft">&#160;</td><td class="mdescRight">Main function. <br /></td></tr>
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><p>Implementation of <a href="https://en.wikipedia.org/wiki/Spirograph">Spirograph</a> </p>
<dl class="section author"><dt>Author</dt><dd><a href="https://github.com/kvedala">Krishna Vedala</a></dd></dl>
<p>Implementation of the program is based on the geometry shown in the figure below:</p>
<p><a href="https://commons.wikimedia.org/wiki/File:Resonance_Cascade.svg"><img src="https://upload.wikimedia.org/wikipedia/commons/3/39/Resonance_Cascade.svg" alt="Spirograph geometry from Wikipedia" style="pointer-events: none; width: 250px" class="inline"/></a> </p>
</div><h2 class="groupheader">Function Documentation</h2>
<a id="a0daa148091ec953809fc172289f773d3"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a0daa148091ec953809fc172289f773d3">&#9670;&nbsp;</a></span>spirograph()</h2>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname">void spirograph </td>
<td>(</td>
<td class="paramtype">double *&#160;</td>
<td class="paramname"><em>x</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">double *&#160;</td>
<td class="paramname"><em>y</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">double&#160;</td>
<td class="paramname"><em>l</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">double&#160;</td>
<td class="paramname"><em>k</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">size_t&#160;</td>
<td class="paramname"><em>N</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">double&#160;</td>
<td class="paramname"><em>rot</em>&#160;</td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td>
</tr>
</table>
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<p>Generate spirograph curve into arrays <code>x</code> and <code>y</code> such that the i^th point in 2D is represented by <code>(x[i],y[i])</code>. </p>
<p>The generating function is given by: </p><p class="formulaDsp">
\begin{eqnarray*} x &amp;=&amp; R\left[ (1-k) \cos (t) + l\cdot k\cdot\cos \left(\frac{1-k}{k}t\right) \right]\\ y &amp;=&amp; R\left[ (1-k) \sin (t) - l\cdot k\cdot\sin \left(\frac{1-k}{k}t\right) \right] \end{eqnarray*}
</p>
<p> where</p><ul>
<li>\(R\) is the scaling parameter that we will consider \(=1\)</li>
<li>\(l=\frac{\rho}{r}\) is the relative distance of marker from the centre of inner circle and \(0\le l\le1\)</li>
<li>\(\rho\) is physical distance of marker from centre of inner circle</li>
<li>\(r\) is the radius of inner circle</li>
<li>\(k=\frac{r}{R}\) is the ratio of radius of inner circle to outer circle and \(0&lt;k&lt;1\)</li>
<li>\(R\) is the radius of outer circle</li>
<li>\(t\) is the angle of rotation of the point i.e., represents the time parameter</li>
</ul>
<p>Since we are considering ratios, the actual values of \(r\) and \(R\) are immaterial.</p>
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[out]</td><td class="paramname">x</td><td>output array containing absicca of points (must be pre-allocated) </td></tr>
<tr><td class="paramdir">[out]</td><td class="paramname">y</td><td>output array containing ordinates of points (must be pre-allocated) </td></tr>
<tr><td class="paramdir"></td><td class="paramname">l</td><td>the relative distance of marker from the centre of inner circle and \(0\le l\le1\) </td></tr>
<tr><td class="paramdir"></td><td class="paramname">k</td><td>the ratio of radius of inner circle to outer circle and \(0&lt;k&lt;1\) </td></tr>
<tr><td class="paramdir"></td><td class="paramname">N</td><td>number of sample points along the trajectory (higher = better resolution but consumes more time and memory) </td></tr>
<tr><td class="paramdir"></td><td class="paramname">num_rot</td><td>the number of rotations to perform (can be fractional value) </td></tr>
</table>
</dd>
</dl>
<div class="fragment"><div class="line"><a name="l00058"></a><span class="lineno"> 58</span>&#160;{</div>
<div class="line"><a name="l00059"></a><span class="lineno"> 59</span>&#160; <span class="keywordtype">double</span> dt = rot * 2.f * M_PI / N;</div>
<div class="line"><a name="l00060"></a><span class="lineno"> 60</span>&#160; <span class="keywordtype">double</span> t = 0.f, R = 1.f;</div>
<div class="line"><a name="l00061"></a><span class="lineno"> 61</span>&#160; <span class="keyword">const</span> <span class="keywordtype">double</span> k1 = 1.f - k;</div>
<div class="line"><a name="l00062"></a><span class="lineno"> 62</span>&#160; </div>
<div class="line"><a name="l00063"></a><span class="lineno"> 63</span>&#160; <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> dk = 0; dk &lt; N; dk++, t += dt)</div>
<div class="line"><a name="l00064"></a><span class="lineno"> 64</span>&#160; {</div>
<div class="line"><a name="l00065"></a><span class="lineno"> 65</span>&#160; x[dk] = R * (k1 * cos(t) + l * k * cos(k1 * t / k));</div>
<div class="line"><a name="l00066"></a><span class="lineno"> 66</span>&#160; y[dk] = R * (k1 * sin(t) - l * k * sin(k1 * t / k));</div>
<div class="line"><a name="l00067"></a><span class="lineno"> 67</span>&#160; }</div>
<div class="line"><a name="l00068"></a><span class="lineno"> 68</span>&#160;}</div>
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