title: How to perform a joint fit of several curves (in Python)?
body: <p>Suppose I'm fitting some data points by a simple linear regression. Now I'd like to perform several <strong>joint</strong> linear regressions for several sets of data points. More specifically, I want one parameter to be equal among all fits, which is schematically depicted here for the y-axis intersection.</p>
  
  <p><a href="https://i.stack.imgur.com/JLAM6.png" rel="nofollow noreferrer" title="y-axis intersection"><img src="https://i.stack.imgur.com/JLAM6.png" alt="y-axis intersection" title="y-axis intersection"></a></p>
  
  <p>After searching Google for some time I could neither find any Python (Scipy) routine which does that, nor any general literature, how one would accomplish this.</p>
  
  <p>Ideally, I want to perform those joint fits not only in the case of simple linear regressions, but also for more general fit functions (for instance, power-law fits with joint exponent).</p>