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For questions pertaining to methods to estimate input parameters based upon output data.

5 votes
Accepted

Is there any theory of the minimum amount of data for tomographic reconstruction?

It's a well-known result that the 2d tomography problem is weakly ill-posed (singular values decay as $O(1/\sqrt{n})$ even with full data and strongly ill-posed (the singular values decay exponentiall …
Brian Borchers's user avatar
9 votes
Accepted

numerical solution of an under-determined linear equation in high dimensions

You want to minimize $\min \| Ax -y \|_{2}^{2} + x^{T}B^{T}Bx=\| Ax -y \|_{2}^{2} + \| Bx \|_{2}^{2}$ Recall that $\| u \|_{2}^{2} + \| v \|_{2}^{2}= \left\| \left[ \begin{array}{c} u \\ v \end{ar …
Brian Borchers's user avatar
9 votes
Accepted

Solving two inverse problems with same solution

You can write your problem as $\min \| Fm - g \|_{2}^{2}$ where $F=\left[ \begin{array}{c} A_{1} \\ A_{2} \\ \alpha I \\ \end{array} \right] $ and $g=\left[ \begin{array}{c} b_{1} \\ b_{2} \\ 0 …
Brian Borchers's user avatar
0 votes

Inverse problem with changing number of variables

There's a large literature on "trans-dimensional" Markov Chain Monte Carlo methods in geophysics where the geophysical model consists of a number of layers and the inversion process adjusts the number …
Brian Borchers's user avatar
4 votes

Objective function scaling in an Inverse Problem

Changing the relative weight of the two terms is equivalent to changing your prior. The fundamental issue here is that you've got a problem with far more parameters to estimate than data points. Y …
Brian Borchers's user avatar
1 vote

Algorithms for radiation treatment planning

There has been a lot of research in this area over the last 20 years. It's appropriate to start by using search engines such as Google Scholar and Web of Science to look for survey and review article …
Brian Borchers's user avatar
3 votes
Accepted

an over view of sparsity promoting inversion techniques

The short answer is that in general this problem is intractable (NP-Hard) with the $\| x \|_{0}$ regularization. Are you willing to consider minimizing $ f(x) + \lambda \| x \|_{1}$ instead? Th …
Brian Borchers's user avatar