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

### 9.3.8: ``differentiate`'

    `differentiate {x|y wrt index|y|x} | {grid wrt x|y}'

Differentiate column data or grid data. Only the ``x`' and ``y`' columns may be differentiated. They may be differentiated either with respect to (``wrt'') the index (forming a first difference) or with respect to the other column. The derivative is done with the backwards-difference algorithm. Grid data may differentiated with respect to ``x`' direction or ``y`' direction. Grid differentiation is done with a centred difference, with endpoints being assigned the derivative of the neighboring interior point (so that the second derivative is zero at the edges of the grid).