 One dimensional minimization in the GNU Scientific Library manual

Official manual: One Dimensional Minimization.

The “Caveats” subsection derives the loss of position accuracy proportional to the square root of function-value relative accuracy near a nonzero minimum with positive second derivative. “Minimization Algorithms” describes golden-section search and its linear contraction. The claims concern standard mathematical precision effects, not an assertion that later software releases were available for a historical examination.