# Any notation for sum of $k$ smallest elements of a vector

Let $x$ be a vector in $\mathbb{R}^n$ and $1 \leq k \leq n$ be given. Is there any commonly used notations for the sum of the $k$ smallest (and largest) elements of $x$? I'm writing a report and don't want to use wordy explanation for something that can be concisely represented.

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Are you asking for notation that examines the vector $[2~~3~~5~~8~~9]$ and would give the two least entries as 2,3? –  Kris Williams Aug 29 '12 at 14:41
@DrKW I'm asking for notation that gives the sum of those two entries, i.e. 5. Note that the vector may be unsorted, so [9 3 5 2 8] will give the same answer (5). –  Truong Aug 29 '12 at 14:45
That looks like a pretty concise definition to me. As long as you make it clear what your notation is and it doesn't conflict with anything else in your report, you should be fine. I'd just keep it simple $s_k(x)$ maybe. –  axblount Aug 29 '12 at 14:54