Chapters: 1: Introduction 2: Simple example 3: Invocation 4: Finer Control 5: XY Plots 6: Contour Plots 7: Image Plots 8: Examples 9: Gri Commands 10: Programming 11: Environment 12: Emacs Mode 13: History 14: Installation 15: Gri Bugs 16: Test Suite 17: Gri in Press 18: Acknowledgments 19: License Indices: Concepts Commands Variables 
10.15: Missing dataMost Gri commands will ignore data points equal to a "missing value." For example, `draw curve ' connects only points which are not equal
(to within 0.01 percent) of the missing value. The curve has holes at
missing data. Initially the missingvalue is set to 1.0e22. You may
alter this value with `set missing value .value. '.
The builtin variable `..missingvalue.. ' stores the current value
of the missingvalue.
Additionally, Gri will ignore anything it reads that is equal to the
string `
Gri also ignores mathematical operations on data items which are equal to
the missing value. Thus, for example, if your missing value is 99 then
the command `
