>>14416439To understand this page you only need to know this:
1) Sum/subraction of matrices is sum/subtraction of its elements
2) In this context, isotropic = all diagonal elements the same (\sigma_m from 5.15). And anisotropic = diagonal elements different (\sigma_{idev}).
I initially thought that this could be interpreted as some sort of covariance matrix, but it can't be. It is only written in terms of sigma and not sigma^2, and its not a Cholesky matrix either.
As for the textbook, I don't know because I haven't checked the content. For all we know it could be how the OP is fucking dumb.
