Yong Fu SU(1); Hai Yun ZHOU(2)
LetE be a Hilbert space,T:D(T)→R(T) be a nonlinear mapping with nonempty set of fixed points.For a lot of nonlinear mappings,the fixed points can be approximating by iteration sequence{x_n}.In the approximating process,a geometric result can be expressed as lim sup_(n→+∞)〈p-p_0,(x_n-p_o)/(||x_n-p_o||)≤0,■p∈F(T).Equvalently, puttingθ_n(p)=arccos〈(p-p_o)/(||p-p_o||),(x_n-p_o)/(||x_n-p_o||)〉,■p∈F(T).then limsup_(n→∞)θ_n(p)≥π/2. This geometric result is said to be an obtuse angle principle.In the relevant condition, the obtuse angle principle holds for nonexpansive mappings,asymptotically nonex- pansive mappings,Lipschitz mappings,accretive mappings,pseudocontractive map- pings,asymptotically pseudocontractive mappings,strictly pseudocontractive map- pings,strongly pseudocontractive mapping,etc.