# What are these bracketing symbols and what do they mean?

What do the matching "L" shapes (near .5 and 20) mean in this forumla?

The document where I found this formula can be found here: http://www.cs.cmu.edu/~hcwong/Pdfs/icip02.ps

• It is the "floor function", meaning the largest integer $\le$ the quantity within. – user641 Apr 9 '13 at 23:22

The definition of Floor is $\lfloor x \rfloor$ = Largest integer less than x. This is very similar to rounding down as $\lfloor 2.3 \rfloor = \lfloor 2.999 \rfloor = 2$. However, the subtlety is that for negative numbers it acts slightly differently, as $\lfloor -1.5 \rfloor = -2$ which might not be what you expect at first.