Fitting

The Fitting GUI consists of these two panes:

• Fit Editor -- Select a fit name and data set, select an exclusion rule, explore and compare library and custom models, and select fit options.
• Table of Fits -- Keep track of all the fits and fit results for the current session.

Fit Editor

The Fit Editor pane is briefly described below.

• New Fit and Copy Fit -- Use New Fit when you are at the beginning of your curve fitting session, or when you are exploring different fit types for a given data set. Clicking New Fit always defaults to the linear polynomial fit type.

• When you are exploring fits of a given type (for example, polynomials), you should click Copy Fit instead of New Fit. Copying a fit retains the current fit type selection and requires fewer steps than creating a new fit each time.

• Fit name -- The name of the current fit. When you click New Fit or Copy Fit, a default fit name is automatically created. You can specify a new fit name by editing this field.
• Data set -- The name of the current data set.
• Exclusion rule -- Lists all the exclusion rules that are compatible with the current data set. An exclusion rule identifies data points to be excluded from the fit.
• Center and scale X data -- If checked, the predictor data is centered at zero mean and scaled to unit standard deviation.
• Type of fit -- Lists the parametric and nonparametric fit types:
• Custom Equations -- Define your own linear or nonlinear equations.

• New equation opens the Create Custom Equation GUI. You should click New equation when you are exploring different custom fit types.

  When you are exploring custom fits that contain similar terms (for example, polynomials of various degrees that do not contain a constant term), you should click Copy equation instead of New equation. Copying a custom equation retains the current custom fit type selection and requires fewer steps than creating a new custom equation each time.

• Exponential -- A one-term or two-term exponential equation.
• Fourier -- Sums of sines and cosines from one sum up to eight sums.
• Gaussian -- Sums of Gaussians up to eight peaks.
• Interpolant -- Linear, nearest neighbor, cubic spline, or shape-preserving interpolation.
• Polynomial -- Polynomial equations from linear to ninth degree.
• Rational -- Ratios of polynomials up to degree five in both numerator and denominator.
• Smoothing Spline -- A piecewise polynomial that varies from linear to cubic. You adjust the level of smoothing with the smoothing parameter. The default parameter value depends on the data and often produces the smoothest fit.
• Sum of Sin Functions-- Sums of sines from one function up to eight functions.
• Weibull -- The two-parameter Weibull distribution.
• Fit options -- Open the Fit Options GUI, which allows you to override default options for linear and nonlinear fitting methods.
• Apply and Immediate apply -- Click Apply to save the fit. Check Immediate apply to save the fit immediately after you select a fit type. When a fit is saved, it is displayed in the Table of Fits pane.
• Results -- Displays detailed results for the current fit including the fit type (model, spline, or interpolant), the fitted coefficients and 95% confidence bounds for parametric fits, and these goodness of fit statistics:
• SSE -- The sum of squares due to error. This statistic measures the deviation of the responses from the fitted values of the responses. A value closer to 0 indicates a better fit.
• R-square -- The coefficient of multiple determination. This statistic measures how successful the fit is in explaining the variation of the data. A value closer to 1 indicates a better fit.
• Adjusted R-square -- The degree of freedom adjusted R-square. A value closer to 1 indicates a better fit. It is generally the best indicator of the fit quality when you add additional coefficients to your model.
• RMSE -- The root mean squared error. A value closer to 0 indicates a better fit.

• Warning messages associated with the fitting process are also displayed in Results.

Table of Fits

The Table of Fits pane is briefly described below.

• Delete fit -- Delete the selected fits. To select multiple fits, hold down the Ctrl key, position the mouse cursor over the rows containing the fit names of interest, and left-click.
• Save to workspace -- Open the Save to Workspace GUI, which allows you to save all the information displayed in the Table to Fits to workspace variables for the selected fit.
• Table options -- Open the Table Options GUI, which allows you to specify the fit-related information that is displayed in the table.