In Curve: Added numerical FD differentiation if derivative is not supplied. Added arc length computation based on the derivative. Added arc length parameterization (but this function is very slow.). In +util: Added fzero_vec.m and integral_vec.m, which call fzero and integral but take vector arguments.

function save_frame = setup_fig_mov(figure_handle,dirname)

    fresh_dir(dirname)

    frame_nr = 0;
    function save_frame_F()
        saveas(figure_handle,sprintf('%s/%s%04d.png',dirname,'fig',frame_nr));
        frame_nr = frame_nr + 1;
    end
    save_frame = @save_frame_F;
end