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).