title: How to make a truncated normal prior: converting pymc2 to pymc3
body: <p>In pymc3 how does one configure a truncated normal prior? In pymc2 it's pretty straightforward (below), but in pymc3 it seems there is no longer a truncated normal distribution available.  </p>
  
  <p>Pymc2:</p>
  
  <pre><code>TruncatedNormal('gamma_own_%i_' % i, mu=go, tau=v_gamma_inv, value=0, a=-np.inf, b=0)
  </code></pre>
  
  <p>Pymc3: ?</p>