Use oriented incidence matrices to connect conservation, cycles, potentials and orthogonal certificates. Signed real flows are allowed; capacities and nonnegative-flow constraints require additional models.
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For a matrix with six columns and rank four, how many independent kernel directions are there?
Network circulations live in edge coordinates, while conservation demands live in vertex coordinates.
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Rank-nullity gives nullity six minus four, or two. The column count is the domain dimension; it must not be replaced by the number of vertex rows.
Why does orthogonality certify a least-norm vector in an affine solution set?
The minimum-flow proof compares a feasible flow with every circulation, not just a few plotted alternatives.
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If f is perpendicular to every allowed displacement z, then ||f+z|| squared equals ||f|| squared plus ||z|| squared. Every nonzero displacement increases the squared norm.