Note that there is significant "noise rectification", i.e. I use a semi-logarithmic plot for better inspection of the data.
#Igor pro curve fitting hold constact plus
This puts up a nice double exponential curve with distinguishable decay constants tau1 and tau2, an "interesting" gaussian peak in the middle, plus some noise and a vertical offset. Place the graph cursors so that they delimit the "end of the curve or profile". Here's a short step-by-step procedure, anyway. I suspect that you might need this from your message (clue "the first point" - this makes sense only if you want a single exponential). You can look up these topics by executing DisplayHelpTopic "weighting" or DisplayHelpTopic "Using a Mask Wave". Keep in mind that fitting an "exponential tail" can be very tricky and give completely wrong results if you have noise or an unknown vertical offset in your data (see below for an example).Īd (2): If you abolutely need to fit everything at once, you can use a mask wave (recommended) and possibly add weighting to your data. For the second fit, you might need to hold some of your coefficients (especially the constant offset), the exp_Xoffset function will probably give wrong results. Adjust the cursors and repeat the curve fitting. Place the cursors to delimit the range of interest at the beginning (small x), then do the curve fit with a SINGLE exponential function. This button is active only when you have the cursors displayed in your graph (bring the graph to the front and then press Ctrl+I. Briefly, in the curve fitting dialog, on the "data options" tab, you can specify the point range manually, or you can click the "cursors" button. This method is also appropriate if you really wanted to fit a single tau parameter, but for different ranges of your data.Īd (1): To learn more about fitting to a subrange, executeĭisplayHelpTopic "Fitting a Subset of the Data" If you intend to fit the data in order to subtract a background, you may need method (2). Method (1) is appropriate if you are interested in the decay constants only (and if you need them both). (2) the hard way is to fit your data using a mask wave (recommended) and also, possibly, weighting
(1) the easy way is to simply fit your data twice with a single exponential function, using a subrange If that's correct, I think there are two ways to go about it: (3) you want to fit your data using two non-contiguous subranges, one at small x and one at large x (2) you suspect that the exponential decay is described by different decay constants tau1 and tau2 (1) you have data that is exponential for small and for large values of x, but not in between I'm not sure if I get your point exactly, but it sounds as if Wide-Angle Neutron Spin Echo Spectroscopy.
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