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From: Sanaloht <san...@gm...> - 2008-09-26 12:24:09
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Hi there! I got a problem and it is not solvable by the fit weight as explained in the help. Second, I'm german, that might lead to funny use of expressions. Be creative in interpreting or ask me. ;) I got a bunch of data points, which each represents a series of tries: 50 tries with 30 fails is represented by 0.6 (60%) the other parameter of the point is a sort of percentile but doesn't really matter. My problem is that not every data point represents the same amount of tries. Maybe 50 tries lead to one data point and the other data point represents 100 tries. What I'd like to have is, that, while the least square process, the residue of every data point is weighed by the amount of tries it represents. Don't know if GnuPlot can do something like that, but I'm thankful for every help! (The weigh explained in the gnuplot help for "fit" just alters the y axis value, I don't think that solves my problem.) Another way to solve my problem could be that I make one data point for every try: I got 50 tries which lead to one data pint with x axis value of 0.6 and y of 0.4, so I make 50 data points with x/y pairs of 0.6/0.4 I did that for every data point but that led to very tiny error values. That is not what I expected. The multiplying of the same data point doesn't lead to more equations to solve the equation. So why is that fit more accurate? So long, Florida Tom -- View this message in context: http://www.nabble.com/Fitting-to-weighed-data-points-tp19654203p19654203.html Sent from the Gnuplot - User mailing list archive at Nabble.com. |
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From: Hans-Bernhard B. <HBB...@t-...> - 2008-09-26 19:33:20
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Sanaloht wrote: > I got a problem and it is not solvable by the fit weight as explained in the > help. You got that wrong. > I got a bunch of data points, which each represents a series of tries: > > 50 tries with 30 fails is represented by 0.6 (60%) the other parameter of > the point is a sort of percentile but doesn't really matter. What exactly does "is represented by" mean here? Are the actual numbers, 50 and 30, present in the data visible by gnuplot, or not? > What I'd like to have is, that, while the least square process, the residue > of every data point is weighed by the amount of tries it represents. Which is *exactly* what the z_error column would do for you, if only you let it. > (The weigh explained in the gnuplot help for "fit" just alters the y axis > value, I don't think that solves my problem.) You misunderstand the documentation, leading to incorrect conclusions. No, the weight doesn't just modify the y axis values. What you need to do is crack open your statistics textbook and learn about counting statistics and their intrinsic error, so you can understand why the solution to your problem is something like fit f(x) 'data.data' using 1:2:(sqrt($2)) via ... |
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From: Sanaloht <san...@gm...> - 2008-09-29 15:59:35
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Damn, that is a nice reply! You're the smartest person I ever met! Actually, the 50 tries and 30 fails are not directly represented in the data. Only the processed pair of two values below 1 indicating percentages. They are the datapoints to which I fit the formula. I can get a third value. It can either be the number of tries or "number of tries/ maximum number of tries". That is, I think, a weight. The GnuPlot help says: " The third item (a column number or an expression), if present, is interpreted as the standard deviation of the corresponding y value and is used to compute a weight for the datum, 1/s**2." I want to let GnuPlot do the weighing for me!!!! But how? I don't have a standard deviation of the y value, so how can I let it be computed? My values are totally correct, no deviation! In which way do I have to supply the standard deviation, or, before you flame me again for this question: How do I have to process my third value to get a standard deviation which I can then use to compute a weight? Well, I guess you don't answer me on this post but maybe someone else has a answer! -- View this message in context: http://www.nabble.com/Fitting-to-weighed-data-points-tp19654203p19726626.html Sent from the Gnuplot - User mailing list archive at Nabble.com. |