In a paper I recently read, the authors use the notation of a subscript plus ($_+$) which is new to me and not explained in the paper. I also did not find anything useful via google. Has anybody a guess, what it means exactly?
Example: A binary variable $z_t \in \{0, 1\}$ describes if state is $on$ (which is $z_t = 1$) at time $t$, or $off$ ($z_t=0$). Each time the state changes, costs of hight $c$ occur. The authors write $c(z_t - z_{t-1})_+$.
As sometimes happens, I found the answer right after posting the question. So for future generations: $(z_t−z_{t−1})_+ = max\{0,z_t−z_{t−1}\}$. There is also a subscript minus, which works analogously.