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Two methods are available for differentiating (finding the derivative of) a curve. Typical uses for differentiating a curve include generating a velocity-time history from a displacement-time record, or pressure-time from impulse-time.
Central Difference
This method sets the output amplitude equal to the slope between the previous and next data points. For the first and last data points in the curve, the code uses the slope between the given point and the previous (for the last point) or next (for the first point) data point. This is the only method available for differentiating curves that do not have a constant spacing in X. In this case, the operation will be performed automatically without presenting the "Differentiate" dialog box.
This method gives results approaching the quadratic interpolation with small differences in spacing, and increasingly poor results for larger variations in spacing.
Quadratic interpolation
This method requires that the input data have a constant spacing. DPlot uses a quadratic interpolating function that fits the amplitude at a given X plus its nearest two neighbors and sets the derivative at this X equal to the slope of the interpolating function.
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See also:
Page url: http://www.dplot.com/help/index.htm?helpid_differentiate.htm
