title: how to specify final value (rather than initial value) for solving differential equations
body: <p>I would like to solve a differential equation in R (with <code>deSolve</code>?) for which I do not have the initial condition, but only the final condition of the state variable. How can this be done?</p>
  <p>The typical code is: <code>ode(times, y, parameters, function ...)</code> where <code>y</code> is the initial condition and <code>function</code> defines the differential equation.</p>