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  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

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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).

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