Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_struct2double”.

  FT_STRUCT2DOUBLE converts all single precision numeric data in a structure
  into double precision. It will also convert plain matrices and
  Use as
    x = ft_struct2double(x)
  Starting from MATLAB 7.0, you can use single precision data in your
  computations, i.e. you do not have to convert back to double precision.
  MATLAB version 6.5 and older only support single precision for storing
  data in memory or on disk, but do not allow computations on single
  precision data. Therefore you should converted your data from single to
  double precision after reading from file.