DCL:GRPH1:SGPACK: User Interface
This is a group of subroutines for the polymarker primitives.
When the internal variable 'LMISS' handled by glpget/glpset
is set to .true., then missing-value handling is performed.
In other words, markers will not be placed on missing values.
Also, by changing the internal variable 'NPMSKIP' (see Section 2.4.4),
settings may be made to skip a number of markers for every one shown.