With the analysis dialogs you can analyse a graph with different methods. By applying a method you create a new graph which is inserted in the active plot.
All analysis functions allows you to select the destination for the resulting data. You can add the result to any existing worksheet/spreadsheet or to a new worksheet/spreadsheet.
Most of the analysis functions can also be applied to a spreadsheet. From the selected columns of the spreadsheet a new column with the resulting values is created.
Table 5.1. Analysis functions of LabPlot
Name | Description | Parameter | Applies to |
Data set operations | If you have at least two graphs in the active plot you can operate on this data set in this dialog. You can add, substract, multiply and divide data sets here. | two datasets | |
Average | With this function you can average over n points of a graph. The number of points is reduced by a factor of 1/n. | number of points to average | everything |
Compress | This function can compress large datasets to less points. You can select whether to sum or average over a certain number of points. | sum or average; number of points | everything |
Smooth | This function does the same as average but for every data point. So you will get a smoothed graph with the same number of data points. | number of points | SPREADSHEET, X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY, X-Y-Z |
Prune | This function reduces the number of data points by just using every n-th point. The resulting number of points is reduced by a factor of 1/n. | number of consecutive points | SPREADSHEET, X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Periodical Functions | This function can be used to reduce a dataset to one period of a function. You can select whether to sum or average. | sum/average; points per period | SPREADSHEET, X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Seasonal | This function can calculate the difference (or sum) of on period to the next one. The period is specified by the number of points in it. | sum/difference; points per period | SPREADSHEET, X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Peak find | This function allows you to find the peaks (also negative peaks) in a data set. The sensitivity for finding peaks can be specified with the parameters threshold and accuracy | positive/negative peaks;threshold (Y-Range); accuracy (X-range) | X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Histogram | With this function you can make a histogram of a graph. That means that the y-range is separated in n bins and every datapoint fitting in one bin is counted. | used Y-range; number of bins | SPREADSHEET, X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY, MATRIX |
Interpolation | Interpolation tries to find a smooth curves through a given set of data points. You can use different types of interpolation to do that : linear, polynomial, cspline, akima. All datapoints in the active region are used for interpolation. | interpolation type; range/number of points for interpolating function | SPREADSHEET, X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Differences | This dialog creates an approximation of the first derivative of a graph. | None | SPREADSHEET, X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Integration | This function can be used to numerical integrate a graph. With the "Add Graph" checkbox you can select whether to add the integrated graph. With the "Show Info" checkbox selected the cumulative sum is shown in a separate window. | baseline/region for integration; sum or area (absolute values) | SPREADSHEET, X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Regression | The regression function can be used to fit a graph with polynomials up to the 10-th order. | weight/model; number of points/range for regression function | X-Y,X-Y-DY,X-Y-DX-DY |
Fourier Tansform | With this function you can calculate the fourier transform of a graph. LabPlot can use the FFTW or GSL library for that. You can select whether to transform forward or backward. | X-values:index/frequency/period; Y-values:magnitude/phase/real part/imaginary part | X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Convolution/Deconvolution | With this function you can calculate the convolution of one graph with another. LabPlot uses the FFTW of GSL for that. It is also possible to deconvolve a set. | X-values:index/same as signal | X-Y, X-Y-DY, X-Y-DY-DY + X-Y, X-Y-DY, X-Y-DY-DY |
Nonlinear Fit | With this function you can fit a graph in a nonlinear fashion. You can select one of 12 different models or any user defined function with up to 9 parameters. Please note that fitting especially exponential models is very sensitive to the initial values. The resulting fit parameter are shown in the bottom field and automatically replaced as initial values for further fitting. The results are added to the plot as label. | fit function;initial values;baseline/region for fitting; range/number of points for fit function | X-Y, X-Y-DY, X-Y-DX-DY, X-Y-DY-DY |
Image Manipulation | In this function you can manipulate matrix or image data of the active plot (for instance a surface plot). LabPlot uses the API of ImageMagick to convert the image with about 50 different methods. | size (height/width) of resulting image | MATRIX,IMAGE |
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