Can't recognize math symbol - bold “minus” above variable

I'm trying to "latex down" some Kalman equations and I'm not able find a way how to make that symbol above k variable in equation "Predict" (1) and (2)

For me, it seems like \bar{} but still I wasn't able to make it look like the same.

• \hat{x}^{-}_{k} for example? It looks like a superscript minus symbol at first glance. – user31729 Apr 14 '14 at 13:17
• I agree with Christian that it appears to be a superscript. If the minus sign is too wide, you could make it P^\textrm{-}_{k}, for example. – Steven B. Segletes Apr 14 '14 at 13:19
• And welcome to TeX.SE! – user31729 Apr 14 '14 at 13:23
• this is almost certainly a superscript minus, and in the example shown, it looks too narrow to me. – barbara beeton Apr 14 '14 at 16:50
• Interesting notation. I was taught to use $\hat{x}(k|k-1)$ for a prediction and $\hat{x}(k|k)$ for a correction. – John Kormylo Apr 14 '14 at 20:33

% arara: pdflatex
$\hat{x}^{-}_{k}=A\hat{x}_{k-1}+Bu_k$