Foundations

Condition Number

The ratio σ_max/σ_min of a matrix's singular values; a measure of how elongated the loss surface is.

Why interviewers ask about it

Feature standardisation, BatchNorm/LayerNorm and Adam's per-parameter scaling are all conditioning fixes. Framing them that way sounds senior.

Factorisation A = UΣVᵀ that exists for any matrix: a rotation, an axis-aligned scaling, then another rotation.

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