I was trying to understand what a positive definite matrix is while reading a reinforcement learning paper today, and I came across this page: http://mathworld.wolfram.com/PositiveDefiniteMatrix.html
The first equation is the one I'm referring to with my question. Does this notation simply mean the real part of the complex matrix that results by evaluating the expression inside the brackets?
Yes, that means real part. It's hard to see, but it's probably supposed to be a "fancy" $$\huge \Re$$