Condition number κ(A) = ‖A‖·‖A⁻¹‖. High κ means nearly parallel lines - a tiny change in b sends x flying. In ML: ill-conditioned Gram matrices make gradient descent unstable.
Condition Number - Interactive Visualization
The condition number κ(A) = ||A|| · ||A⁻¹|| measures how much a linear system amplifies input errors. A high condition number (ill-conditioned matrix) means small errors in b cause large errors in the solution x. Nearly parallel lines in a 2D system give high condition numbers - the intersection point is very sensitive to tiny changes. This is why feature normalization and preconditioning matter in ML.
See two line equations that represent Ax=b geometrically
Adjust matrix entries and watch condition number κ update
Add a small perturbation δb and see the large change in solution δx
Watch lines turn red as they become nearly parallel (ill-conditioned)
Foundation for understanding why batch normalization helps training stability
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