This function estimates the covariance of a tensor random variable. We assume the covariance of the tensor random variable has a seperable Kronecker covariance structure, i.e. \(\boldsymbol{\Sigma}=\boldsymbol{\Sigma}_{m}\otimes\cdots\otimes\boldsymbol{\Sigma}_{1}\). This algorithm is described in Manceur, A. M., & Dutilleul, P. (2013).
kroncov(Tn)
A \(p_1\times\cdots p_m\times n\) data array, where \(n\) is the sample size.
The normalizing constant.
A matrix lists with each element being the individual estimation of the seperable Kronecker covariance element \(\boldsymbol{\Sigma}_m,\ldots,\boldsymbol{\Sigma}_1\).
Manceur, A. M., & Dutilleul, P. (2013). Maximum likelihood estimation for the tensor normal distribution: Algorithm, minimum sample size, and empirical bias and dispersion. Journal of Computational and Applied Mathematics, 239, 37-49.