Gauss-Lucas Theorem: The convex hull of the zeros of a polynomial with complex coefficients contains the zeros of its derivative.
Zeros of P (in red) are bouncing around and the zeros of P', P'', P''', ... nicely dance in the nested convex hulls.
#PDFO_software In memory of late Professor M. J. D. Powell FRS FAA (1936--2015, https://t.co/MLq7j2ZvUU), who passed away five years ago today, we release the first public version (v0.9) of PDFO (Powell's Derivative-Free Optimization solvers): https://t.co/Gj4bLJr1Ay