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.