Function uncovered_cone 

pub fn uncovered_cone(bdirs: &[(f64, f64, f64)]) -> f64

The share of a single orientation’s ill-conditioned cone (|D| < CONE_THRESHOLD) that the directions bdirs still leave ill-conditioned: where sum_t |D_t|^2 < CONE_THRESHOLD^2. 1 for one direction; 0 when the set covers the cone. Repeats of one direction only average noise: three leave 57%. Directions need not be unit length; a zero one is skipped.

Computed over a Fibonacci lattice of 200 000 directions on the sphere, which is the measure of k-space by direction (the kernel depends on direction only); the share is good to about 0.005.