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Screensize: 640 x 480 800 x 600 1024 x 768 1280 x 1024 UserName: Password: Anti-Spam Code: Format Mode: Basic  Help  Prompt  Format: Font Andale Mono Arial Arial Black Book Antiqua Century Gothic Comic Sans MS Courier New Georgia Impact Lucida Console Script MT Bold Stencil Tahoma Times New Roman Trebuchet MS Verdana   Size 1 2 3 4 5 6   Color Black Red Yellow Pink Green Orange Purple Blue Beige Brown Teal Navy Maroon LimeGreen Message: * HTML is OFF * Forum Code is ON Smilies [quote][i]Originally posted by Bobby64[/i] [br]Origin Ver. and Service Release (Select Help-->About Origin): OriginPro 8.5 Operating System: Windows Hi, I would need some advice from specialists of non linear fitting with Origin. Here is my problem: I fit a function through experimental data points and I systematically observe a discrepancy between the fitting results (i.e. the numerical values in the table) and the graph. This graph will show you an example (Bottom: zoom on the low X values) [img]http://www.originlab.com/ftp/forum_and_kbase/Images/Testbob2.jpg[/img] The fittign function I use is a user defined function (called DSE3), with 5 parameters to fit . The last parameter (called DE) is in theory the value of the function at Y=0. As you can see on the table, this value is of 1967.05. However, when I check on the graph, the real value seems to be between 1500 and 1600... SO my questions are : What is the correct value ? Do you have an idea to explain such a difference between the graph and the table ? Do you think that the values indicated in the table are reliable ? In fact, when I use a slightly different function (function DSE), I do not have this kind of problem, i.e. the numerical value of the DE parameter and the graph do match (see below)... [img]http://www.originlab.com/ftp/forum_and_kbase/Images/Testbob3.jpg[/img] So I guess thet the problem may come from the function DSE3 itself, but I do not understand why, since there is no indication of problems with the fitting (chi-2 is reduced, r2 is excellent...) I would appreciate if some of you could give me some advice to understand this, Thanks in advance for your help, Cheers Bobby64 [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.