Simultaneous Orthogonal Matching Pursuit against unembedding directions

Scores and selects specialized attention heads by sparsely reconstructing a batch of real head activations as a small combination of unembedding-matrix (vocabulary) directions via Simultaneous Orthogonal Matching Pursuit (SOMP) -- a multi-sample generalization of the Logit Lens that greedily selects the token direction most correlated with the current residual across all samples at once, rather than one sample at a time.