I came across the following notation, the meaning of which was not explained in the paper itself nor in my usual math bibles, so I'm turning to you. Let me just quote it in its entirety:
Let $A, \delta$ and $c$ be a $1_1$ by $1_2$ matrix, a $1_2$ component vector, and a $1_1$ component vector, respectively.
-- Liew, C.K., 1976. "A Two-Stage Least-Squares Estimation with Inequality Restrictions on Parameters," The Review of Economics and Statistics, MIT Press, vol. 58(2), pages 234-38, May.
I have no clue whatsoever about what things like $1_1$ actually mean. I am quite firm in the notation of theoretical econometrics (at least I think I'm firm...) but I cannot remember that I came across this notation before. Any ideas are highly appreciated.
Cheers, Benjamin
$1$ is the ones vector, a vector with all entries one. You can read about it here. The subscript could further indicate the size of the vector or matrix.