Structure functions of a scalar field, histograms of increments
STFUN = ssf(F,DIM) computes the structure functions of the scalar field
F and the histograms of the scalar increments along the dimension DIM
(with DIM=1, 2, or 'x','y'). If F is an array of fields, the structure
functions are averaged over the fields.
Structure functions of order n are the moments of the scalar increments
as a function of the separation r, <(s(x+r) - s(x))^n>.
The structure STFUN contains the following fields:
- r : separation lengths (in mesh units)
- unitr: unit of separation length (e.g., 'mm')
- scaler : scale (in physical units) of a unit separation
- sf : R-by-ORDER matrix containing the structure functions
of order ORDER.
- sfabs : idem as sf, with absolute values.
- skew: skewness factor.
- flat: flatness factor.
- bin : bins for the histograms
- binwidth: width of a bin
- hsi : (R x BINVEC) matrix containing the histograms of
- pdfsi : normalized histograms (PDF).
- history: remind from which field vsf has been called.
- n: nbre of points used in the computation.
- nfields: nbre of fields used in the computation (given by
STFUN = ssf(S, 'PropertyName', PropertyValue, ...) also specifies the
optional input arguments:
- 'bin', BIN : vector where velocity increments should be bined.
By default, 1000 bins are taken, chosen from the
rms of the first field.
- 'r', R : list of separations delta_r over which increments
are computed, given in mesh units (should be
smaller than the largest extent of the field).
If not specified, a default separation list is
- 'maxorder', ORDER: maximum order of structure function (usually
between 4 and 8). ORDER=4 is taken by default
(although its convergence may not be
By default, ssf considers the values 0 as erroneous, and does not
include them in the histogram. If however the values 0 are to be
included, specify vsf(...,'0');
v = loadvec('*.vc7');
stfun = ssf(filterf(vec2scal(v,'rot')));