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Jul 8, 2011 at 16:32 comment added Romanov This property is called "a tracial property" so I think if a map does not satisfy this property we cannot call it a trace. I am wondering is it possible to classify this category by the property of its trace (analogy to the type of Von Neumann algebras with a "special" trace i.e. finite, semifinite)?
Jul 8, 2011 at 13:33 history edited Ricky
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Jul 7, 2011 at 3:30 comment added Marcel Bischoff It is also true for Ribbon categories, which are in general not symmetric, but just "braided", see eg. Kassel - Quantum Groups.
Jul 6, 2011 at 22:46 comment added David E Speyer If $X$ is $m \times n$ and $Y$ is $n \times m$, then $\mathrm{Tr}(XY) = \mathrm{Tr}(YX)$.
Jul 6, 2011 at 22:26 vote accept Ricky
Jul 6, 2011 at 22:12 comment added Ricky To Qiaochu: I'm completely new to string diagram, so it is possible that my question becomes trivial in that language. I just don't know. To Micheal: what is the trace of a non square matrix? I've always seen the trace of an endomorphism!
Jul 6, 2011 at 22:05 answer added Todd Trimble timeline score: 17
Jul 6, 2011 at 21:56 comment added Michael Hardy Why specify "square" matrices in particular? The occasion for use of this identity with which I am most familiar depends crucially on the matrices not being square.
Jul 6, 2011 at 21:33 comment added Qiaochu Yuan Have you tried drawing the appropriate string diagrams?
Jul 6, 2011 at 21:31 history asked Ricky CC BY-SA 3.0