Gri: `differentiate' command

Gri Commands 1: Introduction 2: Simple example 3: Fancy example 4: Running Gri 5: Programming Gri 6: General Issues 7: X-Y Plots 8: Contour Plots 9: Image Plots 10: Examples 11: Handling Data 12: Gri Commands 13: Gri Extras 14: Evolution of Gri 15: Installing Gri 16: Gri Bugs 17: System Tools 18: Acknowledgments 19: License 20: Newsgroup 21: Concept Index | ## 12.9: The ``differentiate`' Command
    `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).