Save data and other gd objects to a file.
Save the display parameters, the graphic elements,
the coordinates of positions defined by the command GPOS,
the text written by the command GWRITE,
the coefficients of fitted polynomials on a file.
By default, the current input file specified in command GREAD is used.
If the output file already exists, a backup dataset with the extension .gdbackup
is created in the same directory before writing.
If this already exists too, GSAVE fails.
The data are written to a file file in the current directory.
If none of these parameters is given the save set is written to the
current input file specified in command GREAD
Requests that, in addition to the data read from the input file,
the evaluated data are written to the dataset as they were displayed,
i.e. after performing the arithmetic operations specified in the header line.