$\hat C_i v = \lambda (\frac{\gamma}{d} \operatorname*{Trace}(\hat C_j) I + \hat C_j) v$. Figure \[fig:mnistfeats\] shows a sample of results from this procedure for five class pairs (one in each row) and $\gamma=0.5$. In the top row we use class pair $(3, 2)$ and we observe that the eigenvectors are sensitive to the circular stroke of a typical 3 while remaining insensitive to the areas where 2s and 3s overlap. Similar results are seen in the second and third rows where we use class pairs $(8, 5)$ and $(3, 5)$: the strokes we find are along areas used by the first class and mostly avoided by the second class. In the fourth row we use class pair $(8, 0)$. Here we observe two patterns. First, a dot in the center that avoids the 0s. The other 4 detectors consist of positive (red) and negative (blue) strokes arranged in a way that would cancel each other if we take the inner product of the detector with a radially symmetric pattern such as a 0. Similarly in the bottom row with class pair $(4, 9)$, the detector attempts to cancel the horizontal stroke corresponding to the top of the 9, where a 