Fitting to specific curves
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## Fitting to specific curves

QtiPlot include quick access to the most usefull 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 polynome

This command is used to fit a curve which has a linear shape. The results will 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 Bolzmann function

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

Equation 6.3. Bolzmann equation

in which A1 is the low Y limit, A2 is the high Y limit, x0 is the inflexion point and dx is the width.

Figure 6.6. The results of a Fit Bolzmann (sigmoidal).

When the X axis is set to a logarithmic scale, the Fit Bolzmann (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.

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