Single Preceding Vertical Bar

Question

I'm trying to implement the NIST test suite for (p)RNGs (http://csrc.nist.gov/groups/ST/toolkit/rng/documents/SP800-22rev1a.pdf), however I've very quickly run into some notation I'm not familiar with.

The notation in question is:

What does the single vertical bar indicate and how does it modify the calculation to make 2/10 = 0.63245532 rather than 0.2?

Thanks

Answer 1

The specification says (my emphasis):

2.1.3 Test Statistic and Reference Distribution $s_{\text{obs}}$: The absolute value of the sum of the $X_i$ [...] divided by the square root of the length of the sequence.

One thus divides by $\sqrt{10}$ not $10$, and things work out fine.