  Realistic multiport interferometers (beamsplitter meshes) are sensitive to
component imperfections, and this sensitivity increases with size.
Self-configuration techniques can be employed to correct these imperfections,
but not all techniques are equal. This paper highlights the importance of
algorithmic stability in self-configuration. Naive approaches based on
sequentially setting matrix elements are unstable and perform poorly for large
meshes, while techniques based on power ratios perform well in all cases, even
in the presence of large errors. Based on this insight, we propose a
self-configuration scheme for triangular meshes that requires only external
detectors and works without prior knowledge of the component imperfections.
This scheme extends to the rectangular mesh by adding a single array of
detectors along the diagonal.
