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arXiv 2104.08870math.NAcs.NA
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非线性反问题迭代求解器中 Hessian 矩阵的极化张量近似

A polarization tensor approximation for the Hessian in iterative solvers for non-linear inverse problems

F. M. Watson, M. G. Crabb, W. R. B. Lionheart

AI总结:

本文利用极化张量渐近展开构造数据失配项的近似对角 Hessian,并作为拟牛顿方法的初始矩阵,以低成本处理材料对比度饱和非线性,数值验证了其重建效果。

摘要:

对于许多偏微分方程的参数反演问题,当区域中仅包含充分分离的对象时,存在一种涉及“极化张量”的正演问题渐近解。这些张量是夹杂物尺寸和材料对比度的函数,因此描述了非线性的饱和分量。因此,这些渐近展开可以实现对小型孤立对象的快速、稳定重建。本文中,我们通过推导数据失配项的近似对角 Hessian 矩阵,展示了如何将这种渐近级数应用于非线性最小二乘重建问题。Hessian 矩阵通常在处理非线性、生成良好的更新方向方面发挥关键作用,可加速求解趋向可能位于长而弯曲的谷中的全局最小值,但计算成本可能使直接计算不可行。由于极化张量近似假设夹杂物之间具有足够的分离度,我们的近似 Hessian 不考虑反问题中因缺乏叠加性而产生的非线性。然而,它确实考虑了随材料对比度增加,数据变化的非线性饱和。因此,我们建议将其用作拟牛顿格式的初始 Hessian。数值实验以电阻抗层析成像为例对此进行了演示,但该方法也可应用于任何具有等价渐近展开的其他问题。我们给出了关于该近似 Hessian 的准确性和重建性能的数值实验,为该重建方案提供了原理验证。

英文摘要:

For many inverse parameter problems for partial differential equations in which the domain contains only well-separated objects, an asymptotic solution to the forward problem involving 'polarization tensors' exists. These are functions of the size and material contrast of inclusions, thereby describing the saturation component of the non-linearity. As such, these asymptotic expansions can allow fast and stable reconstruction of small isolated objects. In this paper, we show how such an asymptotic series can be applied to non-linear least-squares reconstruction problems, by deriving an approximate diagonal Hessian matrix for the data misfit term. Often, the Hessian matrix can play a vital role in dealing with the non-linearity, generating good update directions which accelerate the solution towards a global minimum which may lie in a long curved valley, but computational cost can make direct calculation infeasible. Since the polarization tensor approximation assumes sufficient separation between inclusions, our approximate Hessian does not account for non-linearity in the form of lack of superposition in the inverse problem. It does however account for the non-linear saturation of the change in the data with increasing material contrast. We therefore propose to use it as an initial Hessian for quasi-Newton schemes. This is demonstrated for the case of electrical impedance tomography in numerical experimentation, but could be applied to any other problem which has an equivalent asymptotic expansion. We present numerical experimentation into the accuracy and reconstruction performance of the approximate Hessian, providing a proof of principle of the reconstruction scheme.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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