Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_warp_error”.

  FT_WARP_ERROR computes the mean distance after linear or non-linear warping
  and can be used as the goalfunction in a 3D warping minimalisation
 
  Use as
    dist = ft_warp_error(M, input, target, 'method')
 
  It returns the mean Euclidian distance (i.e. the residual) for an interative
  optimalization to transform the input towards the target using the
  transformation M with the specified warping method.
 
  See also FT_WARP_OPTIM, FT_WARP_APPLY