title: solve an ODE function of a previous time step (delay differential equation)
body: <p>I have this set of differential equations:</p>
  
  <pre><code>dy/dt = a*y   - b*x*y  
  dx/dt = b*x*y - c*y(t - t_0)
  </code></pre>
  
  <p><code>t_0</code> is a constant time and the term is neglected when <code>t&lt;t_0</code>. How do I solve this in python using numpy/scipy, given initial conditions and all coefficients?</p>
  
  <p>EDIT: the <code>y(t-t_0)</code> is the value of <code>y</code> at the time <code>t-t_0</code>, NOT <code>y</code> times <code>t-t_0</code></p>