Least-Square Fit Setup

NLLS Options

Fit multiple items – Choose the fit behavior when there are multiple items in the model list. This is useful for various applications since it has a profound impact on the results and different modes.

  • Combined – Uses all items together as a single parameterized model that is optimized simultaneously over all specified fit-ranges
  • Sequential – Fits each item on the list one after the other

The first item is fit to the original data. Each additional item is fit to the residual data of the previous fitting. The user may choose to optimize each fit over an individual or all specified fit-ranges.

  • Independent – Each item is independently fit, and its parameters are optimized only over its fit-range

Defaults – Click the ... button to set the default model

Live display – Defines what options are shown as an overlay during live-fitting. These options are best explored by simultaneously observing a running live-fit.

  • Total fit – Shows a slice that constitutes the sum of all references weighted by its fit coefficients
  • Residual (misfit) signal – Displays a slice that represents the difference of the total fit (see above) and the actual data
  • Individual fits  – Presents a slice for each reference
    • Colorize individually – Assigns a different color to each slice and is only available when you select the Individual fits checkbox 

NLLS-Fit Map Options

After pressing the NLLS Fitting button, the map options are automatically shown at the start of a non-linear least squares (NLLS) map computation. 


Fit parameter output

  • Fit parameter values – Creates a map for each fit-parameter
    • Show constant parameter values – When the checkbox is not selected, any fit-parameter that is locked to a fixed value will not produce a map; therefore the map would be a constant value for all pixels

Fit model output

  • Total fit model – Produces an additional spectrum image (SI) data set that shows the entire fit model – The sum of all individual models
  • Individual fit models – Creates additional SI data sets for each model item; the option is not available if there is only one item in the list

Additional output

  • Reduced chi squared – Generates additional maps that shows the reduced chi-squared value (the root of the squared sum overall differences between model and data)
  • Residual signal – Produces an additional SI data set that displays the residual signal (the difference between model and data)


The display options depend on the type of spectrum image and the number of model items in the list. For line scan data, maps become profiles.

  • Show on new Workspace – Shows the mapping results on a separate workspace
    • When not checked, arranges the mapping results on the largest free area of the current workspace
  • Colorize maps – Colorizes the fit-parameter maps using black-to-color gradients (the same color is used either for all parameters of each model item or all parameters of the same name)
  • Add map labels – Adds label annotations to all maps – Use the color-picker button to specify the color of the annotation
  • Add intensity scale – Includes an intensity scale annotation on all maps 
  • Stack profiles – For line scan data, maps become profiles

When this option is checked, it compiles all profile data into a single line-plot display that shows multiple slices. Either all parameters of each model item or the same name are stacked into a single display.