Fitting to specific curves
QtiPlot includes quick access to the most useful functions for fitting.
Fitting to a line
This command is used to fit a curve which has a linear shape.
The results will be given in the Log panel:
Fitting to a polynomial
This command is used to fit a polynomial function to data which has a curvilinear shape. It opens the Polynomial Fit Options dialog, allowing you to choose the curve to fit, the order of the polynomial function to use, the number of points of the resulting curve and the abscissa limits for the fit.
The results of the fit are displayed in the Log panel.
Fitting to a Boltzmann function
This command is used to fit a curve which has a sigmoidal shape. The function used is:
in which A1 is the low Y limit, A2 is the high Y limit, x0 is the inflexion (half amplitude) point and dx is the width.
Fitting to a Logistic function
This command can be used to fit a curve which has a sigmoidal shape. The function used is:
where A1 is the initial Y value, A2 is the final Y value, x0 is the inflexion point (center) and p is the power.
Fitting to a Gauss function
This command is used to fit a curve which has a bell shape. The function used is:
in which A is the height, w is the width, xc is the center and y0 is the Y-values offset.
Fitting to a Lorentz function
This command is used to fit a curve which has a bell shape. The function used is:
in which A is the area, w is the width, xc is the center and y0 is the Y-values offset.
Fitting to a PsdVoigt1 function
This command is used to fit a curve with a Pseudo-Voigt function which is a linear combination of Gaussian and Lorentzian functions:
The parameters of the PsdVoigt1 function have the following meaning: y0 is the Y-values offset, A is the area, w is the width (FWHM), xc is the center and mu is a profile shape factor.
Fitting to a PsdVoigt2 function
This command is used to fit a curve with a Pseudo-Voigt function which is a linear combination of Gaussian and Lorentzian functions with different FWHM:
The parameters of the PsdVoigt2 function have the following meaning: y0 is the Y-values offset, A is the area, wG is the Gaussian FWHM, wL is the Lorentzian FWHM, xc is the center and mu is a profile shape factor.
