[Kst] [Bug 224225] New: 'fit linear weighted' plugin produces different results

freebody.kst at gmail.com freebody.kst at gmail.com
Mon Jan 25 20:58:38 CET 2010


           Summary: 'fit linear weighted' plugin produces different
           Product: kst
           Version: unspecified
          Platform: Compiled Sources
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
        AssignedTo: kst at kde.org
        ReportedBy: freebody.kst at gmail.com

Version:           1.9.0_devel (using Devel)
OS:                Linux
Installed from:    Compiled sources

I tried to plot and fit the same data file using gnuplot and kst, the fit
results are different.

1. create a txt file containing the following data

2  3.5  0.55
4  7.2  0.65
6  9.5  0.74
8  17.1  0.5
10  20.0  0.85
12  25.5  0.6

this is an example from the following web page

2. construct a curve in kst
1.Data --> New Curve...
Choose X from the drop-down list for the X axis vector
Choose Y from the drop-down list for the Y axis vector
Choose DelY from the drop-down list for the +Y error bar
Check Show points in the Appearance panel
Click OK to view the curve

3. curve fitting in kst
Click anywhere on the plot 
Choose Fit --> Y in the appearing context menu
Choose Fit linear weighted(v0.1) in the drop down list of Plugin Selection
Click OK 

4. fit in gnuplot
fit f(x) 'fit.dat' using 1:2:3 via a,b

in kst, gradient:2.2310; intercept:-1.9601

according to the webpage, the result of the weighted linear fit is
gradient:2.23; intercept:-1.528. gnuplot confirms the same result.

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