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Given a list of log-likelihood $\log\mathcal{L}_i$ for $ i \in [1, N]$, if I want to compute the average log-likelihood correctly, I need

$$ \langle \log \mathcal{L} \rangle = \log\left(\frac{1}{N}\sum_{i=1}^{N}e^{\log\mathcal{L}_i}\right).$$ (taking the mean of the logs themselves is not the same).

However, for large likelihoods I quickly run into numerical problems (the reason for using log-likelihoods in the first place..)

Is there any methods to improve the numerical stability? Or am I missing something here...

Greg
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    See https://stats.stackexchange.com/search?q=log+overflow. Or https://stats.stackexchange.com/search?q=log+underflow. – whuber Oct 26 '17 at 21:18

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