Operations

Working with Operations

Various operations can be applied to curves in a graph. By default operations are applied only in the graph, not to the worksheet data. These include:

• Translate and scale
• Move and delete data points
• Derivative, integral
• Smooth, denoise
• Interpolation/extrapolation
• Add, subtract, multiply, etc. with another curve
• Other calculations (manual)

Curves that have operations appear blue in the legend:

A list of all the operations applied to the selected curves appears in the properties window of the curve under the Operations tab. Operations can be individually enabled/disabled, moved, removed or edited.

Use Operations ‣ Apply Permanently to apply the operations to the worksheet data. Operations ‣ Apply to Copy makes a copy of the curve and applies the operations to it, removing them from the original curve. Operations can also be copied and pasted between curves.

Available Operations

Translate

Shift horizontally and/or vertically (add a constant).

Scale

Scale horizontally and/or vertically (multiply by a constant).

Differentiate

Three methods are available:

Central Differences

Derivative is the average of the slopes between each point and its two closest neighbors.

Savitzky-Golay

Calculate derivative using Savitzky-Golay smoothing (see below).

derivative: order of the derivative to calculate

points: number of points to use on either side of the data point

order: Order of the polynomial used, usually leave this at 3

Polynomial

Calculate n-th derivative from fitting a n-th order polynomial to a given number of points around each data point.

Integrate

Two methods are available:

Trapezoidal

Integrate using the trapezoidal rule.

Splines

Calculate integral of a spline fitted to the data.

order: polynomial order of the spline

Smooth

Four smoothing methods are available:

Adjacent averaging

Data are smoothed using moving average. You can set the number of points on either side, as well as a smoothing window to emphasize the central values in the average.

Savitzky-Golay

Smoothing using a Savitzky-Golay filter. You can set the number of points on either side, and the polynomial order.

Splines

Smooth using a spline curve. Set the spline order.

Order filter

Each point is replaced by the chosen percentile of a given number of data points around it. The default is a median filter (percentila is 0.5).

Interpolate/Extrapolate

Four interpolation methods are available: linear, splines, B-splines and PCHIP.

For extrapolation, you also have the choice to use data from another dataset or from the current fit function.

Dataset Calculations

Add, subtract, multiply or divide with another curve.

Manual

Enter expressions to apply manual calculations to the x and y values of the curve.

Edit Points

Drag data points to move, double click to remove.

Denoise

Denoise a signal using wavelets. Parameters are the same as MATLAB’s wden function.