Gri: missing values

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.