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Fix forecasting slides
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sarahCobey committed Jul 26, 2016
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Expand Up @@ -91,19 +91,20 @@ <h3>Nonlinear forecasting</h3>
</section>

<section>
<h3>Complex attractors</h3>
<h3>Dynamics may be chaotic</h3>
<img class="stretch" src="images/lorenz.png">
</section>

<section>
<h3>Why short-term?</h3>
<h3>Predictions with chaos: short shelf life</h3>
<p>Trajectories in chaotic attractors diverge
<p> $$ \lvert \delta \textbf{Z}(t)\rvert \approx e^{\lambda t}\lvert\delta\textbf{Z}_0\rvert$$
<p> $\lambda$ is the Lyapunov exponent
<p> (so with chaos, $\lambda>0$)
</section>

<section>
<section>
<h3>How to forecast</h3>
<ul>
<li>Choose an embedding dimension $E$ and lag $\tau$</li>
Expand All @@ -113,9 +114,9 @@ <h3>How to forecast</h3>
<li>See where predictee's $E+1$ nearest neighbors wind up $t$ steps into the future</li>
<li>Measure correlations $\rho$ between predictee's observed future state and neighbors' weighted predictions</li>
</ul>
</section>
</section>

<section>
<section>
<h3>Choosing $E$ and $\tau$</h3>
<p>An unsolved problem
<p>Use $E$ (and $\tau$) that yield best predictions</p>
Expand All @@ -124,6 +125,9 @@ <h3>Choosing $E$ and $\tau$</h3>
<a href="http://www.nature.com/nature/journal/v344/n6268/abs/344734a0.html">Sugihara and May 1990</a>
</div>
</section>
</section>



<section>
<h3>Observational noise v. chaos</h3>
Expand Down Expand Up @@ -246,7 +250,7 @@ <h3>Predictive fitness models</h3>
<br>
<p>A simple predictive model estimates the fitness $f$ of virus $i$ as</p>
<p>$$\hat{f}_i = \beta^\mathrm{ep} \, f_i^\mathrm{ep} + \beta^\mathrm{ne} \, f_i^\mathrm{ne}$$</p>
<p>where $f_i^\mathrm{ep}$ measures cross-immunity via substitutions at epitope sites and $f_i^\mathrm{ep}$ measures mutational load via substitutions at non-epitope sites</p>
<p>where $f_i^\mathrm{ep}$ measures cross-immunity via substitutions at epitope sites and $f_i^\mathrm{ne}$ measures mutational load via substitutions at non-epitope sites</p>
<div class="citation">
<a href="http://www.nature.com/nature/journal/v507/n7490/full/nature13087.html">&#321;uksza and L&auml;ssig 2014</a>
</div>
Expand All @@ -257,7 +261,7 @@ <h3>Model selection</h3>
<img src="images/luksza_models.png">
<div class="citation">
<a href="https://www.google.com/?ion=1&espv=2#q=predictive%20fitness%20luksza">
Luksza and Lassig 2014
&#321;uksza and L&auml;ssig 2014
</a>
</div>
</section>
Expand All @@ -267,7 +271,7 @@ <h3>Performance</h3>
<img class="stretch" src="images/prediction_ll.jpg">
<div class="citation">
<a href="https://www.google.com/?ion=1&espv=2#q=predictive%20fitness%20luksza">
Luksza and Lassig 2014
&#321;uksza and L&auml;ssig 2014
</a>
</div>
</section>
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