A class of preconditioned iterative methods, i.e., preconditioned generalized accelerated overrelaxation （GAOR） methods, is proposed to solve linear systems based on a class of weighted linear least squares problems...A class of preconditioned iterative methods, i.e., preconditioned generalized accelerated overrelaxation （GAOR） methods, is proposed to solve linear systems based on a class of weighted linear least squares problems. The convergence and comparison results are obtained. The comparison results show that the convergence rate of the preconditioned iterative methods is better than that of the original methods. Furthermore, the effectiveness of the proposed methods is shown in the numerical experiment.展开更多
Investigating the relationships between vegetation dynamic and edaphic factors provide management insights into factors affecting the growth and establishment of plant species and vegetation communities in saline area...Investigating the relationships between vegetation dynamic and edaphic factors provide management insights into factors affecting the growth and establishment of plant species and vegetation communities in saline areas.The aim of this study was to assess the spatial variability of various vegetation communities in relation to edaphic factors in the Great Salt Desert,central Iran.Fifteen vegetation communities were identified using the physiognomy-floristic method.Coverage and density of vegetation communities were determined using the transect plot method.Forty soil samples were collected from major horizons of fifteen profiles in vegetation communities,and analyzed in terms of following soil physical and chemical characteristics:soil texture,soluble Na+concentration,sodium adsorption ratio(SAR),electrical conductivity(EC),pH,organic matter content,soluble Mg2+and Ca2+concentrations,carbonate and gypsum contents,and spontaneously-and mechanically-dispersible clay contents.Redundancy analysis was used to investigate the relationships between vegetation dynamic and edaphic factors.The generalized linear method(GLM)was used to find the plant species response curves against edaphic factors.Results showed that plant species responded differently to edaphic factors,in which soluble sodium concentration,EC,SAR,gypsum content and soil texture were identified as the most discriminative edaphic factors.The studied plant species were also found to have different ecological requirements and tolerance to edaphic factors,in which Tamarix aphylla and Halocnemum strobilaceum were identified as the most salt-resistant species in the region.Furthermore,the presence of Artemisia sieberi was highly related to soil sand and gypsum contents.The results implied that exploring the plant species response curves against edaphic factors can assist managers to lay out more appropriate restoration plans in similar arid areas.展开更多
We prove that any linear multi-step method G1^T of the form ∑k=0^mαkZk = T∑k=0^mβkJ^-1↓ΔH（Zk） with odd order u （u≥ 3） cannot be conjugate to a symplectic method G2^T of order w （w 〉 u） via any generalize...We prove that any linear multi-step method G1^T of the form ∑k=0^mαkZk = T∑k=0^mβkJ^-1↓ΔH（Zk） with odd order u （u≥ 3） cannot be conjugate to a symplectic method G2^T of order w （w 〉 u） via any generalized linear multi-step method G3^T of the form ∑k=0^mαkZk = T∑k=0^mβkJ^-1↓ΔH（∑l=0^mγklZl）. We also give a necessary condition for this kind of generalized linear multi-step methods to be conjugate-symplectic. We also demonstrate that these results can be easily extended to the case when G3^T is a more general operator.展开更多
基金supported by the National Natural Science Foundation of China (No. 11071033)the Fundamental Research Funds for the Central Universities (No. 090405013)
文摘A class of preconditioned iterative methods, i.e., preconditioned generalized accelerated overrelaxation （GAOR） methods, is proposed to solve linear systems based on a class of weighted linear least squares problems. The convergence and comparison results are obtained. The comparison results show that the convergence rate of the preconditioned iterative methods is better than that of the original methods. Furthermore, the effectiveness of the proposed methods is shown in the numerical experiment.
文摘Investigating the relationships between vegetation dynamic and edaphic factors provide management insights into factors affecting the growth and establishment of plant species and vegetation communities in saline areas.The aim of this study was to assess the spatial variability of various vegetation communities in relation to edaphic factors in the Great Salt Desert,central Iran.Fifteen vegetation communities were identified using the physiognomy-floristic method.Coverage and density of vegetation communities were determined using the transect plot method.Forty soil samples were collected from major horizons of fifteen profiles in vegetation communities,and analyzed in terms of following soil physical and chemical characteristics:soil texture,soluble Na+concentration,sodium adsorption ratio(SAR),electrical conductivity(EC),pH,organic matter content,soluble Mg2+and Ca2+concentrations,carbonate and gypsum contents,and spontaneously-and mechanically-dispersible clay contents.Redundancy analysis was used to investigate the relationships between vegetation dynamic and edaphic factors.The generalized linear method(GLM)was used to find the plant species response curves against edaphic factors.Results showed that plant species responded differently to edaphic factors,in which soluble sodium concentration,EC,SAR,gypsum content and soil texture were identified as the most discriminative edaphic factors.The studied plant species were also found to have different ecological requirements and tolerance to edaphic factors,in which Tamarix aphylla and Halocnemum strobilaceum were identified as the most salt-resistant species in the region.Furthermore,the presence of Artemisia sieberi was highly related to soil sand and gypsum contents.The results implied that exploring the plant species response curves against edaphic factors can assist managers to lay out more appropriate restoration plans in similar arid areas.
基金Acknowledgements. We would like to thank the editors for their valuable suggestions and corrections. This research is supported by the National Natural Science Foundation of China （Grant Nos. 10471145 and 10672143）, and by Morningside Center of Mathematics, Chinese Academy of Sciences.
文摘We prove that any linear multi-step method G1^T of the form ∑k=0^mαkZk = T∑k=0^mβkJ^-1↓ΔH（Zk） with odd order u （u≥ 3） cannot be conjugate to a symplectic method G2^T of order w （w 〉 u） via any generalized linear multi-step method G3^T of the form ∑k=0^mαkZk = T∑k=0^mβkJ^-1↓ΔH（∑l=0^mγklZl）. We also give a necessary condition for this kind of generalized linear multi-step methods to be conjugate-symplectic. We also demonstrate that these results can be easily extended to the case when G3^T is a more general operator.
