Peak Fitting Analysis Template *
You can use the Peak Fitting analysis template to approximate multiple instances of a peak model function to a pre-defined data set. A number of pre-defined model functions are available to do this. The template is based on the Non-Linear Curve Fitting analysis object.
Step 2: Baseline
The model consists of one model function per peak and a baseline. FlexPro determines the baseline through linear regression of a series of points. If you select the option Automatic, you only need to specify the number of points. FlexPro then determines their position automatically. Otherwise, you can also set the baseline manually. Use the enter key to select where you want to apply the cursors in the diagram. You can also select points that are not on the curve by disabling the option Bind Cursor To Curve on the toolbar under the diagram. The option Calculate Baseline lets you display the approximated baseline, and Delete Baseline allows you to remove it again, if necessary.
FlexPro can account for the baseline in three ways:
•Include baseline as variable component in model
Includes the baseline with variable parameters in the peak model. The parameters set here are only used as initial values.
•Include baseline as static component in model
Includes the baseline with the fixed parameters set here in the peak model.
•Subtract baseline from source data
The baseline is not included in the model, but rather is subtracted from the data before curve fitting.
Step 3: Model, Specify Peaks, Options
A number of pre-defined peak models are available. The Maximum number of function calls setting allows you to limit the number of iterations for the fitting. You can automatically determine the positions of the peaks. You only need to specify the No. of peaks. The peaks are set via local maxima and/or minima, depending on what you select for the Type. The Hysteresis specifies by which amount the curve to the left and right of the data set must rise or fall so that a local maximum or minimum is accepted. You can also set the peaks manually by using the cursor to set markers at the particular locations in the curve and then clicking on Calculate. You can use Delete Peaks to remove all peaks from the diagram.
You can now select various Display Options:
•Residuals
displays the course of the curve of the fitting residual.
•2nd Derivative
displays the second derivative of the data set.
•Peak Curves
displays the approximated peak curves.
•Result
displays a table with the parameters of the individual peak models.
•Statistics
displays statistics to assess the quality of the fitting.
•Prediction Band
presents the prediction band for the adapted peak curve in the diagram. A 95% confidence interval is the Y range for a given X value that contains the true Y value with 95% probability.
•Confidence Band
presents the confidence band for the adapted peak curve in the diagram. The 95% prediction band makes a statement about the scattering of the data to be analyzed. If you were to collect more data points, 95% of the points would fall within the range of the prediction band.
Step 4: Algorithm, Weighting, Scaling, Initial Values, Settings
The fields Algorithm, Weighting, Scaling and Settings have the same functions as those of the Non-Linear Curve Fitting analysis object. The Initial Values list displays the initial values for the individual model functions. In the Shared column, you can set which parameters are to have the same value for all peaks. You can force all peaks to have the same width, for instance.
FPScript Functions Used
See Also
Statistical Output Options for Non-Linear Curve Fitting
* This analysis template is not available in FlexPro View.