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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 rainbowkoala[/i] [br]Origin Ver. and Service Release (Select Help-->About Origin): OriginPro 9.0.0 (32-bit) Operating System: win7 Hello, I hope you can help me with the following problem: The experimental data points can be fitted with two peaks. How to get the wanted fitting result using user defined function as follows: [img]http://www.originlab.com/ftp/forum_and_kbase/Images/wanted.gif[/img] The symbols are experimental data points and the blue solid lines are the total #64257;tting results. The #64257;tting peak A (green line) and the #64257;tting peak B (red line) are down. However, I can only got the fitting result as follows: [img]http://www.originlab.com/ftp/forum_and_kbase/Images/result.gif[/img] The symbols are experimental data points and the blue solid lines are the total #64257;tting results. The #64257;tting peak A (green line) and the #64257;tting peak B (red line) are down. In orther words, I want to lower Peak A and improve Peak B. The following are the fitting steps. The experimental data points can be fitted with two peaks. In order to plot the two fitting peaks and the cumulative fit peak on source graph, I defined a user peak function and set parameters as in the following screenshot: [img]http://www.originlab.com/ftp/forum_and_kbase/Images/HN1.gif[/img] Then I used the defined fitting function to do non-linear fitting. Select analysis:Fitting:Nonlinear Curve Fit:Open dialog:menu to bring up the NLFit dialog box. In the Function Selection part, choose the function I defined, In the Settings: Advanced: Replica: Number of Replicas part, choose 1, so the experimental data points can be fitted with two peaks, as shown in figure below: [img]http://www.originlab.com/ftp/forum_and_kbase/Images/HN settings.gif[/img] The fiting parameters are as follow: [img]http://www.originlab.com/ftp/forum_and_kbase/Images/HN parameters.gif[/img] The original data and the detailed data in MS-Word are a little large, so I have sent them to the tech@originlab.com and quote this post. The defined function is as follows: y=a*sin(d*atan((x*b)^c*cos(3.14/(2*(1-c)))/(1+(x*b)^c*sin(3.14/(2*(1-c))))))/(1+2*(x*b)^c*sin(3.14/2*(1-c))+(x*b1)^(2*c))^(d/2) In order to simplify the function, the function can also be written as follows: y=a*sin(d*A)/(1+2*(x*b)^c*sin(3.14/2*(1-c))+(x*b1)^(2*c))^(d/2) A= atan((x*b)^c*cos(3.14/(2*(1-c)))/(1+(x*b)^c*sin(3.14/(2*(1-c))))) [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.