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PIVMat 3.02

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PIVMat 3.02

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27 Apr 2006 (Updated )

A PIV Post-processing and data analysis toolbox

ssf (PIVMat Toolbox)
ssf (PIVMat Toolbox)
PIVMat Function Reference<< Prev | Next >> 
ssf
Structure functions of a scalar field, histograms of increments

Description
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 
                  scalar increments. 
  - 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 
                  LENGTH(S)). 
 
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 
                     used. 
   - 'maxorder', ORDER: maximum order of structure function (usually 
                        between 4 and 8). ORDER=4 is taken by default 
                        (although its convergence may not be 
                        guaranteed). 
 
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'); 
 
Example
 
   v = loadvec('*.vc7'); 
   stfun = ssf(filterf(vec2scal(v,'rot'))); 
 
See Also
vsf, vsf_disp, histf, corrf, specf. 
 
Published output in the Help browser 
   showdemo ssf 

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