Chapters: 1: Introduction 2: Simple example 3: Invocation 4: Finer Control 5: X-Y 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 data Most 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 missing-value is set to 1.0e22. You may alter this value with ``set missing value .value.`'. The built-in variable ``..missingvalue..`' stores the current value of the missing-value. Additionally, Gri will ignore anything it reads that is equal to the string ``NaN`' or ``Inf`'. These are produced by matlab, C, and other programs when dividing by zero, etc. 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 ``x += 1`' will not change the values equal to -99 to -98, since this would have the side-effect of making the datum no longer be considered missing.