##Tr([Q,P])## and Ballentine Problem 6.3

[strangerep]

[...] taking the trace (and seeing that it gives an infinite sum of terms each of which is $i \hbar$) is simple.

No, it's not. An infinite sum like $(\sum_{n=0}^\infty 1)$ is divergent.

 

[PeterDonis]

An infinite sum like $(\sum_{n=0}^\infty 1)$ is divergent.

Yes, I know that. I'm just saying that that infinite sum is what formally taking the trace of the infinite identity matrix gives you. I think something like that is what Ballentine intends to illustrate with the problem under discussion.