V = randvec returns a synthetic 2D vector field with a k^(-5/3) spectrum,
random phase and zero 2D divergence. The size of the vector field is
256x256 by default. V has the same structure as vector fields loaded by
loadvec, with arbitrary units.
V = randvec(N) returns a field of size N*N.
V = randvec(N,NF) returns an array of NF fields.
V = randvec(N,NF,SLOPE) imposes a spectrum k^-SLOPE (-5/3 by default).
V = randvec(N,NF,SLOPE,NC,NL) does the same, but specifies the small
scale NC and large-scale NL cut-offs (in units of vector mesh).
By default, NC=3 and NL=N/3. For k<NL, the spectrum is k^2. For k > NC,
the spectrum falls gaussianly.