PHT Interactive Analysis User Manual - (V9.0)

3.5.2) PIA Spectrum Multi-Fit Facility

The PHT Interactive Analysis software offers for the evaluation of PHT-S spectra a Multiple Fitting package to perfom the simultaneous fitting of several curves to a given data set. It is an adaptation to PIA from an original package kindly offered to us by the ISO-SWS Instrument Dedicated Team.

Figure 1 shows the multiple fitting window, as it appears directly after its call. On the right side, a plot of the input data is given, the right side is divided into several areas, which are described below.


FIGURE 1: PIA multiple fitting window 

The righthand side of the window can be divided into 3 regions:

The general purpose is to fit to the input data (or to a region in it) a combination of functions which describe the data. As a basis function a polynom is given, default is a 1st degree polynom. One of the frames of Region B allows the degree of the polynom to be changed. When doing so, the first parameters in Region C change their definitions.

The other functions to be added are extracted from the option "+" in the functions row. Several functions can be chosen:

  • gauss
  • (sin(x)/x )^2
  • exponential
  • cauchy function
  • double fermi



    Whenever a function is chosen, the fitting parameters corresponding to this function are defined in the parameter definition's list and the functions taken are inserted in the frame labelled "+ function" in Region B.

    In order to activate the fit button, start parameters have to be defined by clicking on the par_in button. On top of Region C options for the start parameters are given. This makes it possible to write start values directly into the fields, or to use the mouse by clicking on the cursor button. In this case a new frame appears below the plot on the lefthand side of the window. For every function the parameters can be indicated by clicking the mouse on the data plot. Note that you have to confirm each set of parameters for every function so that they are included in the parameters list. After the numbers are filled in, the ok button on top of the parameters list in region C has to be clicked on, before applying for fitting with the fit button on the functions row. Please note that the parameters can be fixed to the value shown by clicking on the far righthand buttons of the parameter's list. In this case they are not changed during the fitting.

    The fit procedure updates the parameter list with the fitted parameters. The fitted curve is drawn on top of the data points, and a plot of the residuals is given below the data plot.

    This procedure can be repeated by changing parameters, fixing them, etc. Also the choice of using only certain parts of the data is possible through the new range button on the functions row.

    History of this Content File:
    Date Author Description
    24/07/1996 Carlos Gabriel (ESA/VILSPA-SAI) First Version
    10/06/1997 Carlos Gabriel (ESA/VILSPA-SAI) Update (V6.3)