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fix: sampleCHRR returns NaN when the equality system is square #696

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Merged
edkerk merged 1 commit into from
Aug 26, 2026
Merged

fix: sampleCHRR returns NaN when the equality system is square #696

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12 changes: 8 additions & 4 deletions analysis/sampleCHRR.m
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Original file line number Diff line number Diff line change
Expand Up @@ -85,10 +85,14 @@

% Particular solution v0 and nullspace basis N: v = v0 + N*x.
% v0 is ANY particular solution; the sampled flux distribution is invariant to
% its choice and to the nullspace basis, so MATLAB's '\' (a sparse basic
% solution) and the Python reference's lstsq (minimum-norm solution) sample the
% same polytope despite returning different v0.
v0 = Aeq \ beq;
% its choice and to the nullspace basis, so the minimum-norm solution used here
% and the Python reference's lstsq sample the same polytope.
% lsqminnorm rather than '\': Aeq is square whenever the number of metabolites
% plus the number of folded-in fixed reactions equals the number of reactions,
% and it is then rank-deficient, for which '\' returns NaN. Those NaNs travel
% into the polytope and surface much later as a misleading "empty interior"
% error from sampleChebyshevCenter.
v0 = lsqminnorm(Aeq, beq);
N = null(Aeq);
d = size(N, 2);

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