Allow spectrum='nonzero' with no zero eigenvalue (#112)#157
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The previous unconditional `if n_zero == 0: raise ValueError` blocked legitimate use cases like hippocampal-subfield analyses where the weight matrix has no kernel (no medial wall). Simply removing the guard, as proposed in #112, would silently corrupt the spectrum='all' branch (it would drop the largest eigenvalue instead of a zero one). Make the guard branch-aware: spectrum='all' still requires a zero eigenvalue and raises a clearer error pointing at spectrum='nonzero'; spectrum='nonzero' now accepts kernel-free matrices and returns all eigenvalues. Adds two regression tests covering both branches. Co-authored-by: Jordan DeKraker <jordandekraker@users.noreply.github.com>
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Supersedes #112.
@jordandekraker's bug report is real: a weight matrix with no kernel (e.g. hippocampal-subfield surfaces with no medial wall) shouldn't raise. The original PR removed the guard outright, but that silently corrupts the
spectrum='all'branch —mask_zero.argmax()returns0when nothing is True, so the code drops the largest eigenvalue instead of a zero one.This PR makes the guard branch-aware:
spectrum='all'still requiresn_zero >= 1and now raises a clearer message pointing atspectrum='nonzero'.spectrum='nonzero'accepts kernel-free matrices and returns all eigenvalues.Plus two regression tests covering both branches.
@jordandekraker is credited as Co-author on the squashed commit.
Test plan
pytest brainspace/tests/test_null_models.py→ 6 passed.