title: PyMC3 model does not generate sample data close to the observed data
body: <p>I have created an MCMC model using PyMC3 following the steps provided in the following example:</p>
  
  <p><a href="https://pymc-devs.github.io/pymc3/notebooks/LKJ.html" rel="nofollow noreferrer">https://pymc-devs.github.io/pymc3/notebooks/LKJ.html</a></p>
  
  <p>The results, I get is similar to the following image:
  <a href="https://i.stack.imgur.com/RJPjl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RJPjl.png" alt="enter image description here"></a></p>
  
  <p>The simulated samples are following nicely the same pattern that observed data have. However, the range in X and Y is much smaller. Does anyone know how I can have samples that cover a range of numbers similar to the observed data?</p>