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Say we model $\mathbf{x}_t \in \mathbb{R}^d$ as a linear combination of factor loadings: $$\mathbf{x}_t = \mathbf{E}\mathbf{F}_t + \boldsymbol{\epsilon}_t, \qquad \boldsymbol{\epsilon}_t \sim \mathcal{N}(\mathbf{0}, \mathbf{B})$$ Let $\mathbf{E} \in \mathbb{R}^{d\times p}$, $\mathbf{F}_t \in \mathbb{R}^p$, and $\mathbf{B} \in \mathbb{R}^{d\times d}$ be random, and take $\mathbf{B}$ to be diagonal. The latter allows correlation structure to be captured by the factors rather than by the residuals. To fit this model using Bayesian inference, we place priors on the columns of $\mathbf{E}$ and on the $\mathbf{F}_t$s. To keep the model conjugate, we can use Gaussian priors on both parameters; thus, the posteriors for both parameters will be Gaussian.

Many sources including this and this say that the above model is nonidentifiable since we can always reparameterize $\mathbf{E}' = \mathbf{ER}$ and $\mathbf{F_t}' = \mathbf{S}\mathbf{F}_t$, where $\mathbf{RS} = \mathbf{I}$. Does this mean that an algorithm that tries to get MAP estimates for the parameters $\mathbf{E}$ and $\mathbf{F_t}$ given the likelihood and priors above (say, coordinate ascent) will not converge unless we place some type of constraint on $\mathbf{E}$?

Vivek Subramanian
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    Factor values F are not "parameters", only loadings are "parameters" which are estimated by a factor analysis algorithm. F values cannot be identified because - to rephrase what the sources say nontechnically - F (factors) and e (uniquenesses) are tied with each other and neither of them is not known on case level t. Yes, to compute F some way a constraint is needed, but the constraint is not the part of factor analysis model or an algorithm to estimate loadings (which is the task of factor analysis). – ttnphns May 15 '15 at 11:05
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    Take my comment is non-bayesian. – ttnphns May 15 '15 at 11:07
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    And it is true that many loading matrices can satisfy the model, they are arbitrarily or [analytically rotated versions](http://stats.stackexchange.com/q/151653/3277) of each other. – ttnphns May 15 '15 at 11:28

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