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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 AJOKi[/i] [br]Hello, I'm a new user of Origin, so far it's been very helpful to analyze my data however I'm not very good with math and I have some questions that I would like to ask about the Weibull function for data fitting. I have some experimental data that I want to fit to a mathematical model, so far the best model is the SWeibull2 function, as it is shown by the R2, X2 and fitting curve that appears after analysis with origin. In the information that appears about the model, it shows the sigmoidal function: Y = A-(A-B)*exp -(kx)^d and mentions that has four parameters. However, I've reading about the Weibull model and came across different equations for this particular cumulative function, for example Y = Y0*(1-exp –(t-T/a)^b), or Y = 1-exp-(x/lambda)^k or Y = 1-(1-g)*exp-(kx/t)^b (they look similar but the exponential core function is different and I haven't been able to transform one into the other). I was wondering if you could explain to me or link to me a couple of references where is clearly explained and in simplified terms if possible, from which four parameter cumulative Weibull function Origin derivates its SWeibull2 function to fit a set of data? Can you please explain step by stem parameterization to obtain Y = A-(A-B)*exp -(kx)^d ? I understand that variables and parameter letters may change, and that the commonly referred "b" parameter in classical Weibull functions is the "d" parameter in Origin with the previous mentioned formula. If I were to write this formula on a scientific paper for the scientific community, Which form of notation is recommended? I hope my questions are clear and I would appreciate very much any information you can give me. [8D] Kind regards! AJ-->thanks [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.