7.4 Data analysis

This section describes the data analysis functions of KUPLOT. Apparently variables can also be used to calculate averages and analyse data sets. The contents of a variable or result of an expression can be displayed with the command 'eval'. Another wide area of data analysis is to fit a theory function to a data set. The least square fitting functions of KUPLOT are discussed in the next chapter. As example for this chapter we use a subsection of the diffuse scattering data displayed in previous examples. The data are shown in Figure 7.3. The circles mark positions of maxima found in the data set by the command 'smax'.

  

Figure 7.3: Marking of maxima within a plot

A maximum determined by 'smax' is defined as a point where all nneighbouring points have smaller y- or z-values compared to the reference point. The value of n is the second parameter of the 'smax' command, the first is the data set number. The maxima marked in Figure 7.3 were determined with 'smax 1,3' assuming we are dealing with data set one. The command 'ptyp' allows one to select a symbol analog to 'mtyp' to mark the positions of the determined maxima. Furthermore the positions of the found maxima are displayed on the screen. The output for our example is shown below:

   Found maxima data set   1 (ifen =   3) :

      No.        pos. x       pos. y         value
      --------------------------------------------------
        1         .600        4.200             272.778
        2         .650        3.750             567.111
        3        1.000        3.950             273.889
        4        1.400        3.700             509.667
        5        1.450        4.200             156.778

You might verify these coordinates as the marked positions in figure 7.3. Other functions allow the user to determine the integral or mean values of a given area of the data set. Next we will determine the integral of the left diffuse peak in figure 7.3. This is done using the command

    inte 1, .423750, .903750, 3.4716, 3.99168

The first parameter specifies the data set number followed by the area to be integrated given as x_min, x_max, y_min and y_max. If those last 4 parameters are omitted, the complete current plotting window is used. The screen output of this command is:

    Integration result for data set   1 :
       x-range    :    .4238     to    .9038
       y-range    :    3.472     to    3.992
       Integral   :    57.06     +-    .3650      (    100 pkt)

The command 'mean' with similar parameters can be used to calculate mean values and standard deviations in the given region. The region above was determined using the 'mouse' functions (see 5).

  

Figure 7.4: Fourier transform of box function