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removed valueError for nonzero eigenvalues #112

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removed valueError for nonzero eigenvalues #112

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3 changes: 0 additions & 3 deletions brainspace/null_models/moran.py
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Original file line number Diff line number Diff line change
Expand Up @@ -99,9 +99,6 @@ def compute_mem(w, n_ring=1, spectrum='nonzero', tol=1e-10):
mask_zero = ev_abs < tol
n_zero = np.count_nonzero(mask_zero)

Copilot AI Feb 9, 2026

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With the ValueError removed, spectrum='nonzero' now returns all eigenvectors when n_zero == 0 (i.e., nothing is filtered by mask_zero). That contradicts the function’s contract of removing the (at least one) zero/constant mode from the doubly-centered matrix and can change downstream behavior (e.g., component count becomes n_vertices instead of the expected <= n_vertices-1). Consider treating the smallest-|eigenvalue| entry as zero when n_zero == 0 (e.g., set mask_zero[ev_abs.argmin()] = True) so the constant mode is still removed even when numerical precision/tol prevents exact zeros.

Suggested change
# If no eigenvalue is below tolerance but spectrum=='nonzero', still
# remove at least one mode (the one with smallest |eigenvalue|),
# corresponding to the constant component of the doubly centered matrix.
if spectrum == 'nonzero' and n_zero == 0:
idx_min = ev_abs.argmin()
mask_zero[idx_min] = True
n_zero = 1

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if n_zero == 0:
raise ValueError('Weight matrix has no zero eigenvalue.')

# Multiple zero eigenvalues
if spectrum == 'all':
if n_zero > 1:
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