mmin (moving minimum verb)
The mmin verb returns the N-item moving minimum of its numeric right argument, with nulls treated as the minimum value. The first N items of the result are the minimums of the terms so far, and thereafter the result is the moving minimum.
q)3 mmin 0N -3 -2 1 -0W 0 0N 0N 0N -3 -0W -0W q)3 mmin 0N -3 -2 1 0N -0W / null is the minimum value 0N 0N 0N -3 0N 0N
For a complete list of functions, see the kdb+ Function Reference.