Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

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.

share|improve this question
    
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
1  
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

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.