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ztrans [2010/06/11 02:04] (current)
jochen created
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 +====== ztrans ======
  
 +===== Motivation =====
 +Under certain circumstances (e.g. data that is arbitrarily scaled and comes from several sources has to be compared), one way to normalize (re-scale) the data is to apply z-transformation (setting the mean of values in the desired dimension to 0 and the standard deviation to 1).
 +
 +===== Function reference ('help ztrans'​) =====
 +<​file> ​ ztrans ​ - perform z-transformation on time course
 + 
 +  FORMAT: ​      [ztc, zf, zsh] = ztrans(tc [, dim [, tp]])
 + 
 +  Input fields:
 + 
 +        tc          time course data
 +        dim         ​temporal dimension (default: first non-singleton)
 +        tp          time points (indices of dim to use for normalization)
 + 
 +  Output fields:
 + 
 +        ztc         ​z-transformed time course
 +        zf          z-transformation factor
 +        zsh         ​z-transformation shift
 + 
 +  See also psctrans</​file>​
 +
 +===== Usage examples =====
 +  * z-transforming a single time-course (e.g. of a region or voxel):<​code matlab>​ztc = ztrans(tc);</​code>​
 +  * z-transformation of an entire VTC (ensuring that dimension is 1):<code matlab>​vtc.VTCData = ztrans(vtc.VTCData,​ 1);</​code>​
 +  * z-transformation of 4D-NII VoxelData (ensuring that dimension is 4):<code matlab>​nii.VoxelData = ztrans(nii.VoxelData,​ 4);</​code>​
 +  * also obtaining the information about the scaling factor and shift:<​code matlab>​[ztc,​ zfactor, zshift] = ztrans(tc);</​code>​
 +  * only using values where no experimental condition in an SDM is active:<​code matlab>% find timepoints to use
 +tp = all(abs(sdm.SDMMatrix(:,​ 1:​sdm.FirstConfoundPredictor-1)) < 0.1, 2);
 +
 +% apply z-transformation with those as normalization basis
 +vtc.VTCData = ztrans(vtc.VTCData,​ 1, tp);</​code>​
ztrans.txt ยท Last modified: 2010/06/11 02:04 by jochen