The PGPLOT X-axis options string. The global parameter will be
updated to include the PGPLOT "L" axis option at the start.
This option means that logarithmic style axis labels and tick
marks will be plotted. The READF command will automatically
remove any "L" characters at the start of this string since it
assumes that they have been put there by CLOG, and fresh data
read in will not be logarithmic. If data are naturally
logarithmic, the "L" should be placed other than at the start
of the string to make an "L" option that will not be modified
It is not intended that this parameter be set by you when
CLOG is executed.
The value will be written to the global parameter PONGO_XOPT.