title: Gnuplot fit error : Singular matrix in Givens()
body: <p>I want to fit a function with a dataset using gnuplot.</p>
  
  <p>I use a data set example, in the file "data":</p>
  
  <pre><code>1 2
  5 4
  6 5
  7 8
  </code></pre>
  
  <p>If I do in gnuplot</p>
  
  <pre><code>&gt;f(x) = a*x+b
  &gt;fit f(x) "data" via a,b
  </code></pre>
  
  <p>It works just good, (and with this example I get a≃0.855 and b≃0.687)</p>
  
  <p>Now what I really want to do is to fit the function <code>floor(a*x+b)</code>. So I tried exactly the same way</p>
  
  <pre><code>&gt;f(x) = floor(a*x+b)
  &gt;fit f(x) "data" via a,b
  </code></pre>
  
  <p>And I get the output</p>
  
  <pre><code> Iteration 0
   WSSR        : 8                 delta(WSSR)/WSSR   : 0
   delta(WSSR) : 0                 limit for stopping : 1e-005
   lambda   : 0
  
  initial set of free parameter values
  
  a               = 1
  b               = 1
           Singular matrix in Givens()
           error during fit
  </code></pre>
  
  <p>Googling it didn't help me, I also tried to find if there was some contraindication using fit with floor but again I didn't find anything.</p>
  
  <p>Has someone an idea?</p>
  
  <p>Note : I use Gnuplot 4.6 patchlevel 0, built for Windows 32bit</p>