The QtiPlot Handbook
Prev | Chapter 6. Analysis of data and curves | Next

# 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.

Figure 6-4. The results of a Fit Linear.

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. Results are be given in the Log panel

Figure 6-5. The results of a Fit Polynomial..., showing the initial data, the curve added to the plot, and the results 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:

Equation 6-3. Boltzmann equation

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.

Figure 6-6. The results of a Fit Boltzmann (sigmoidal).

When the X axis is using a logarithmic scale, the Fit Boltzmann (sigmoidal) command uses the Logistical equation for fitting:

Equation 6-4. Logistic dose response equation

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:

Equation 6-5. Gauss equation

in which A is the height, w is the width, xc is the center and y0 is the Y-values offset.

Figure 6-7. The results of a Fit Gaussian.

## Fitting to a Lorentz function

This command is used to fit a curve which has a bell shape. The function used is:

Equation 6-6. Lorentz equation

in which A is the area, w is the width, xc is the center and y0 is the Y-values offset.

Figure 6-8. The results of a Fit Lorentzian.

Prev | Home | Next
The Fit Wizard | Up | Multi-Peaks fitting