https://sourceforge.net/p/gnuplot/support-requests/254/2020-09-20T20:02:46.609000ZRecent changes to 254: Fit complex function2020-09-20T20:02:46.609000Z2020-09-20T20:02:46.609000ZAlexander Stanglhttps://sourceforge.net/u/fahrrad13/https://sourceforge.net5d7f7ca3f570fce3e43fecd34cc787fe8f5da957

<div class="markdown_content"><p>Thanks for your reply. <br/> This blogspot describes bascially the same approach. So for gnuplot duplicating the data (or reading it in twice with CoreUtilities) and fitting real and complex data via multi-branch fit seems to be the best option with good fitting results.</p></div>

2020-09-18T23:09:39.550000Z2020-09-18T23:09:39.550000ZEthan Merritthttps://sourceforge.net/u/sfeam/https://sourceforge.net023db73511ed7d708ecb9de14350041725bbe40c

<div class="markdown_content"><p>Not my field of expertise, but I found this:<br/> <a href="https://stevethemoose.blogspot.com/2014/04/levenbergmarquardt-fitting-to-complex.html" rel="nofollow">https://stevethemoose.blogspot.com/2014/04/levenbergmarquardt-fitting-to-complex.html</a></p></div>

2020-09-18T08:42:39.806000Z2020-09-18T08:42:39.806000ZAlexander Stanglhttps://sourceforge.net/u/fahrrad13/https://sourceforge.net07cb834be1c94a0bceaa1512f3d2557fddcb9976

<div class="markdown_content"><p>Hello everyone,</p> <p>I would like to fit a complex function. However, also in the fit function "using" requires floating numbers and cannot handle complex numbers. <br/> My data file has 3 columns: x, real component of f(x), imaginary component of f(x)<br/> I have managed so far with a work around using multibranch fitting:</p> <div class="codehilite"><pre><span></span><span class="s s-Atom">i=</span><span class="p">{</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">}</span> <span class="s s-Atom">#imaginary</span> <span class="s s-Atom">unit</span> <span class="s s-Atom">#a</span> <span class="s s-Atom">complex</span> <span class="s s-Atom">function</span> <span class="nf">f</span><span class="p">(</span><span class="s s-Atom">x</span><span class="p">)</span> <span class="o">=</span> <span class="p">(</span><span class="s s-Atom">a</span><span class="o">+</span><span class="s s-Atom">b</span><span class="o">*</span><span class="s s-Atom">i</span><span class="p">)</span><span class="o">*</span><span class="s s-Atom">x</span> <span class="s s-Atom">#multibranch</span> <span class="nn">fit</span><span class="p">:</span> <span class="s s-Atom">#fit</span> <span class="s s-Atom">first</span> <span class="s s-Atom">real</span> <span class="s s-Atom">part</span><span class="p">,</span> <span class="s s-Atom">then</span> <span class="s s-Atom">imaginary</span> <span class="s s-Atom">part</span> <span class="nf">g</span><span class="p">(</span><span class="s s-Atom">x</span><span class="p">,</span><span class="s s-Atom">y</span><span class="p">)</span> <span class="o">=</span> <span class="p">(</span><span class="s s-Atom">y</span><span class="o">==</span><span class="mi">0</span> <span class="s s-Atom">?</span> <span class="nf">real</span><span class="p">(</span><span class="nf">f</span><span class="p">(</span><span class="s s-Atom">x</span><span class="p">))</span> <span class="s s-Atom">:</span> <span class="nf">imag</span><span class="p">(</span><span class="nf">f</span><span class="p">(</span><span class="s s-Atom">x</span><span class="p">)))</span> <span class="s s-Atom">fit</span> <span class="nf">g</span><span class="p">(</span><span class="s s-Atom">x</span><span class="p">,</span><span class="s s-Atom">y</span><span class="p">)</span> <span class="s2">"file.dat"</span> <span class="s s-Atom">u</span> <span class="mi">1</span><span class="p">:-</span><span class="mi">2</span><span class="s s-Atom">:</span><span class="p">(</span><span class="nf">column</span><span class="p">(</span><span class="o">-</span><span class="mi">2</span><span class="p">)</span><span class="o">==</span><span class="mi">0</span> <span class="s s-Atom">?</span> <span class="err">$</span><span class="mi">2</span><span class="s s-Atom">:</span><span class="err">$</span><span class="mi">3</span><span class="p">)</span> <span class="s s-Atom">via</span> <span class="s s-Atom">a</span><span class="p">,</span><span class="s s-Atom">b</span> </pre></div> <p>however, to do this I needed to duplicate the data in the file to be able to run this multibranch fit (block 0 is used to fit the real part, block 1 for the imaginary part).</p> <p>Now my question:<br/> is there anyway to fit a complex function more elegant and/or is there anyway to read in the data file twice without having to duplicate the data within the file?</p> <p>For the latter I also managed using CoreUtils with the "cat" command:</p> <div class="codehilite"><pre><span></span><span class="n">fit</span> <span class="k">g</span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">)</span> <span class="s1">'&lt; cat "file.dat" "newlines.txt" "file.dat"'</span> </pre></div> <p>where "newlines.txt" contains only two empty new lines, so that the second time file .dat is loaded as a new block.</p> <p>Thanks for your help!<br/> Best,<br/> Alex</p> <p>For more info about CoreUtils in gnuplot see e.g. here:<br/> <a href="https://stackoverflow.com/questions/11549004/gnuplot-plot-data-from-two-files-in-one-x-coordinate-in-other-y" rel="nofollow">https://stackoverflow.com/questions/11549004/gnuplot-plot-data-from-two-files-in-one-x-coordinate-in-other-y</a><br/> <a href="http://gnuplot.10905.n7.nabble.com/combining-data-from-different-input-files-td3528.html" rel="nofollow">http://gnuplot.10905.n7.nabble.com/combining-data-from-different-input-files-td3528.html</a><br/> <a href="http://gnuwin32.sourceforge.net/packages/coreutils.htm" rel="nofollow">http://gnuwin32.sourceforge.net/packages/coreutils.htm</a></p></div>