Commit e1ac92f9 by Ying-Qiu Zheng

### Update 2021JUL21.md

parent 78164835
 ... ... @@ -4,12 +4,16 @@ ### Model formulation Suppose $\mathbf{X}^{H}, \mathbf{X}^{L}$ are $N \times V$ feature matrices (e.g. connectivity between $N$ thalamus voxels and $V$ whole brain voxels). Note that they can have different dimensions in practice. To keep notations uncluttered, we suppose the number of voxels in high- and low-quality images are the same for a given subject. Now we assume $\mathbf{X}^{H}, \mathbf{X}^{L}$ share the same latent variable $Y$, which is a $N \times K$ binary matrix representing the voxels' classes. For a single voxel, suppose $\mathbf{y}_{n} \sim \text{multinomial}(\mathcal{\pi})$, and $p(\mathbf{x}^{L}_{n}|y_{nk}=1) = \mathcal{N}(\mu_{k}, \Sigma_{k}^{L})$. To use high-quality data to inform the inference on low-quality data, we assume $p(\mathbf{x}^{H}_{n}|y_{nk}=1, \mathbf{U}) = \mathcal{N}(\mathbf{U}\mathbf{x}^{H}_{n}|\mu_{k}, \Sigma_{k}^{H})$ where $\mathbf{U}^{T}\mathbf{U} = \mathbf{I}$. The complete likelihood can be written as For a single voxel, suppose $\mathbf{y}_{n} \sim \text{multinomial}(\mathcal{\pi})$, and $p(\mathbf{x}^{L}_{n}|y_{nk}=1) = \mathcal{N}(\mu_{k}, \Sigma_{k}^{L})$. To use high-quality data to inform the inference on low-quality data, we assume $p(\mathbf{x}^{H}_{n}|y_{nk}=1, \mathbf{U}) = \mathcal{N}(\mathbf{U}\mathbf{x}^{H}_{n}|\mu_{k}, \Sigma_{k}^{H})$ where $\mathbf{U}^{T}\mathbf{U} = \mathbf{I}$. The complete log-likelihood can be written as math \log p(\mathbf{x}^{H}_{n}, \mathbf{x}^{L}_{n}, \mathbf{y}_{n}|\mathbf{U},...\mathbf{\pi}, \mathbf{\mu}_{k},...\mathbf{\Sigma}^{H}_{k},...\mathbf{\Sigma}^{L}_{k},...) = \prod_{k=1}^{K}(\pi_{k}\mathcal{N}(\mathbf{x}^{L}_{n}|\mu_{k},\Sigma_{k}^{L})\mathcal{N}(\mathbf{Ux}^{H}_{n}|\mu_{k},\Sigma_{k}^{H}))^{y_{nk}}  The marginal distribution of $\mathbf{x}_{n}^{L}, \mathbf{x}_{n}^{H}$ is math \log p(\mathbf{x}^{H}_{n}, \mathbf{x}^{L}_{n} | \mathbf{U},...\mathbf{\pi}, \mathbf{\mu}_{k},...\mathbf{\Sigma}^{H}_{k},...\mathbf{\Sigma}^{L}_{k},...)=\sum_{k=1}^{K}\pi_{k}\mathcal{N}(\mathbf{x}^{L}_{n}|\mu_{k},\Sigma_{k}^{L})\mathcal{N}(\mathbf{Ux}^{H}_{n}|\mu_{k},\Sigma_{k}^{H})  ... ...
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!