title: What does the error message "w = 0 in Givens();" mean when trying curve fitting in gnuplot?
body: <p>I keep having the <code>w = 0 in Givens();</code> error message when I try to use <code>gnuplot</code> built-in curve fitting feature.</p>
  
  <p>What I do is trying to fit experimental data to a certain mathematical model in <code>gnuplot</code>.
  I define the model function <code>s(x)</code>:</p>
  
  <pre><code>gnuplot&gt; z(x)=(x-mu)/be
  gnuplot&gt; s(x)=(k/be)*exp(-z(x)-exp(-z(x)))
  </code></pre>
  
  <p>Then I plot the actual data and the model function to get an initial guess for the model parameters:</p>
  
  <p><img src="https://i.stack.imgur.com/YKpEO.png" alt="initial"></p>
  
  <p>Then I adjust the initial guess:</p>
  
  <pre><code>gnuplot&gt; k=2.6; mu=-8.8; 
  gnuplot&gt; replot
  </code></pre>
  
  <p>To obtain a pretty fine picture:</p>
  
  <p><img src="https://i.stack.imgur.com/0BLR7.png" alt="initial-adjusted"></p>
  
  <p>Then I try to precisely fit the curve:</p>
  
  <pre><code>gnuplot&gt; fit s(x) '701_707_TRACtdetq.log30.hist1.txt' u 2:6 via k,be,mu
  </code></pre>
  
  <p>And what I get is the single iteration and a error message:</p>
  
  <pre><code> Iteration 0
   WSSR        : 3.85695           delta(WSSR)/WSSR   : 0
   delta(WSSR) : 0                 limit for stopping : 1e-05
   lambda   : 0.223951
  
  initial set of free parameter values
  
  k               = 2.6
  be              = 1
  mu              = -8.8
  /
  
   Iteration 1
   WSSR        : 0.0720502         delta(WSSR)/WSSR   : -52.5315
   delta(WSSR) : -3.7849           limit for stopping : 1e-05
   lambda   : 0.0223951
  
  resultant parameter values
  
  k               = 2.03996
  be              = 0.777868
  mu              = -8.87082
           w = 0 in Givens();  Cjj = 3.37383e-196,  Cij = 2.54469e-192
  </code></pre>
  
  <p>And the curve pretty fit:</p>
  
  <p><img src="https://i.stack.imgur.com/2UsEB.png" alt="fit"></p>
  
  <p>What does that error means and how would I get the fit process going?</p>