In this study,the problem of bundle adjustment was revisited,and a novel algorithm based on block matrix Cholesky decomposition was proposed to solve the thorny problem of self-calibration bundle adjustment.The innova...In this study,the problem of bundle adjustment was revisited,and a novel algorithm based on block matrix Cholesky decomposition was proposed to solve the thorny problem of self-calibration bundle adjustment.The innovation points are reflected in the following aspects:①The proposed algorithm is not dependent on the Schur complement,and the calculation process is simple and clear;②The complexities of time and space tend to O(n)in the context of world point number is far greater than that of images and cameras,so the calculation magnitude and memory consumption can be reduced significantly;③The proposed algorithm can carry out self-calibration bundle adjustment in single-camera,multi-camera,and variable-camera modes;④Some measures are employed to improve the optimization effects.Experimental tests showed that the proposed algorithm has the ability to achieve state-of-the-art performance in accuracy and robustness,and it has a strong adaptability as well,because the optimized results are accurate and robust even if the initial values have large deviations from the truth.This study could provide theoretical guidance and technical support for the image-based positioning and 3D reconstruction in the fields of photogrammetry,computer vision and robotics.展开更多
共同基金选择是资产配置关注的重要问题之一。本文提出了基金网络下的共同基金选择模型,该模型将基金重仓持股的网络权重矩阵作为惩罚项引入参数估计中,能够限定彼此相连基金的业绩alpha(α)的差异。在此基础上,本文评估了基金网络对基...共同基金选择是资产配置关注的重要问题之一。本文提出了基金网络下的共同基金选择模型,该模型将基金重仓持股的网络权重矩阵作为惩罚项引入参数估计中,能够限定彼此相连基金的业绩alpha(α)的差异。在此基础上,本文评估了基金网络对基金业绩的影响,并结合错误发现率(FDR)方法提出了基于网络调整的共同基金选择策略。实证采用中国2016年1月至2020年12月的596只共同基金数据样本进行分析,研究发现:①近5年中国基金的持股具有高度重合度,使得基金业绩之间存在较高的关联性;②基金网络与基金业绩之间存在“马太效应”,即基金网络对正α基金存在正向作用,而对负α基金存在负向作用;③通过与其他基金选择方法做对比,本文提出的基于网络调整的共同基金选择模型能够有效地剔除基金网络对基金业绩的影响,选出真正具有选股能力的基金。本文结果不仅可为基金间的共同持股行为提供新的解释,还可为投资者或Fund of Funds(FOF)基金经理的投资决策提供新的视角。展开更多
对矩阵的奇异值分解(SVD,Singular Value Decomposition)进行了分析。推导证明了奇异值分解和M-P广义逆矩阵之间的关系,得出奇异值分解的广义逆矩阵为矩阵的M-P广义逆;分析了奇异值分解和线性方程组最小范数最小二乘解的关系,推导了应...对矩阵的奇异值分解(SVD,Singular Value Decomposition)进行了分析。推导证明了奇异值分解和M-P广义逆矩阵之间的关系,得出奇异值分解的广义逆矩阵为矩阵的M-P广义逆;分析了奇异值分解和线性方程组最小范数最小二乘解的关系,推导了应用奇异值分解进行秩亏网平差解算的平差解算公式和精度估算公式;推导了加权最小二乘最小范数解的奇异值分解解算问题,扩展了奇异值分解求解未知参数最小范数最小二乘解;最后通过秩亏网算例进行了解算,验证了方法的正确性和矩阵分解的有效性。展开更多
基金National Natural Science Foundation of China(Nos.41571410,41977067,42171422)。
文摘In this study,the problem of bundle adjustment was revisited,and a novel algorithm based on block matrix Cholesky decomposition was proposed to solve the thorny problem of self-calibration bundle adjustment.The innovation points are reflected in the following aspects:①The proposed algorithm is not dependent on the Schur complement,and the calculation process is simple and clear;②The complexities of time and space tend to O(n)in the context of world point number is far greater than that of images and cameras,so the calculation magnitude and memory consumption can be reduced significantly;③The proposed algorithm can carry out self-calibration bundle adjustment in single-camera,multi-camera,and variable-camera modes;④Some measures are employed to improve the optimization effects.Experimental tests showed that the proposed algorithm has the ability to achieve state-of-the-art performance in accuracy and robustness,and it has a strong adaptability as well,because the optimized results are accurate and robust even if the initial values have large deviations from the truth.This study could provide theoretical guidance and technical support for the image-based positioning and 3D reconstruction in the fields of photogrammetry,computer vision and robotics.
文摘共同基金选择是资产配置关注的重要问题之一。本文提出了基金网络下的共同基金选择模型,该模型将基金重仓持股的网络权重矩阵作为惩罚项引入参数估计中,能够限定彼此相连基金的业绩alpha(α)的差异。在此基础上,本文评估了基金网络对基金业绩的影响,并结合错误发现率(FDR)方法提出了基于网络调整的共同基金选择策略。实证采用中国2016年1月至2020年12月的596只共同基金数据样本进行分析,研究发现:①近5年中国基金的持股具有高度重合度,使得基金业绩之间存在较高的关联性;②基金网络与基金业绩之间存在“马太效应”,即基金网络对正α基金存在正向作用,而对负α基金存在负向作用;③通过与其他基金选择方法做对比,本文提出的基于网络调整的共同基金选择模型能够有效地剔除基金网络对基金业绩的影响,选出真正具有选股能力的基金。本文结果不仅可为基金间的共同持股行为提供新的解释,还可为投资者或Fund of Funds(FOF)基金经理的投资决策提供新的视角。
文摘目的研究易层贴敷疗法对骨性关节炎(OA)中滑膜炎症因子及基质金属蛋白酶表达的影响。方法 30只新西兰大白兔,随机分为正常组、模型对照组及治疗组;模型对照组及治疗组通过切断兔左后肢前交叉韧带获得OA模型,术后6周外用易层贴敷;术后8周处死动物,取滑膜行Western Blot及荧光定量PCR检测IL-1β、MMP-1及MMP-13的含量及表达。结果 Western Blot测定模型对照组滑膜中MMP-1及MMP-13含量明显高于治疗组,正常组中含量最低;荧光定量PCR测定模型对照组中MMP-1及MMP-13的表达量最高,正常组最低;正常组滑膜中IL-1β表达明显最低,模型对照组与治疗组之间无统计学差异。结论易层贴敷疗法能有效抑制滑膜中MMP-1及MMP-13的表达,从而降低了软骨基质的降解,缓解OA的进程,仍需进一步研究其具体的作用靶点,完善其作用机制。
文摘对矩阵的奇异值分解(SVD,Singular Value Decomposition)进行了分析。推导证明了奇异值分解和M-P广义逆矩阵之间的关系,得出奇异值分解的广义逆矩阵为矩阵的M-P广义逆;分析了奇异值分解和线性方程组最小范数最小二乘解的关系,推导了应用奇异值分解进行秩亏网平差解算的平差解算公式和精度估算公式;推导了加权最小二乘最小范数解的奇异值分解解算问题,扩展了奇异值分解求解未知参数最小范数最小二乘解;最后通过秩亏网算例进行了解算,验证了方法的正确性和矩阵分解的有效性。
