ExportDX - Write a DX field in DX native format.
   
   USAGE:

   header = ExportDX(fname, mesh)
   header = ExportDX(fname, mesh, Ndata)
   header = ExportDX(fname, mesh, Ndata, Edata)

   INPUT:

   fname is a string, 
         the basename of the DX header file, as well as the 
         basename of the various ASCII output files, and also
         the name of the resulting DX field

   mesh  is a MeshStructure

   Ndata is a cell array,
         it contains position-dependent data; it has the form
         {name1, array1, name2, array2, ...}, where the names
         are strings with no spaces and the arrays are real-valued
         data arrays;  Ndata can be empty.
         
   Edata is a cell array,
         it contains connection-dependent data and has the same
         form as Ndata

   OUTPUT:

   header is a cell array of strings,
          it contains the DX header file content

   NOTES:

   *  ExportDX writes the DX field to fname.dx, and the field 
      object is named fname.  Each array in Ndata or Edata is
      written to a separate file (fname-arayname.dat) and is 
      added as a component of the DX field.

   *  Currently, this routine can only handle element types
      of 'lines', 'triangles', 'tetrahedra' or 'cubes'.

 WriteDataFile - Write data to a file with a text header.
   
   USAGE:

   WriteDataFile(fname, text, data)
   WriteDataFile(fname, text, data, basefmt)
   WriteDataFile(fname, text, data, basefmt, append)

   INPUT:

   fname is a string, 
         the name of the file
   text  is a cell array of strings, 
         the text header to write at the beginning of the file; 
         it can be empty
   data  is m x n, (numeric)
         the data to write; the data is written as passed, 
         m rows of n columns each
   basefmt is a string, (optional, default = '%25.16e')
         the printf-style format to use on each value;  if this 
         argument is left out or is the empty string '', the default
         value for reals is used; if the argument is
         the string 'integer', the format used is '%10d';
         other values are used without change
   append is a scalar,  (optional, default = 0)
          if nonzero, the output file is appended to instead of 
          overwritten

   OUTPUT:  none

 WriteMPSOrientations - Write orientations in MPS format.
   
   USAGE:

   header = WriteMPSOrientations(filename,orient, hinfo)

   INPUT:

   filename is a string, 
            the name of the output file
   orient   is m x n, 
            the array of orientations to write
   hinfo    is a cell array,
            it contains header information; options are:
 
   'Weights',          array

   'Hardnesses',       array

   'Parameterization', string  [required]

   'Angles',           string  ('degrees'|'radians')

   OUTPUT:

   header is a cell array of strings,
          it contains the MPS (material point simulator) 
          header information; the header and data are
          written to the requested file