fn solve_small(a: &[f64; 9], b: &[f64; 3], n: usize) -> Option<[f64; 3]>Expand description
Solve A x = b for small n (≤ LM_MAX_N) by Gaussian elimination with
partial pivoting. a is row-major n×n. Returns None if singular. Only
the first n entries of the inputs and the result are used.