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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 Dr.S[/i] [br]Dear all, I am not too familiar with origin C but i tried my best in order to fit some data with a sum function based on cranks laws of diffusion. I would like to fit the following function to my data: y = M (1-8/pi²*SUM(1/(2n+1)² * e^(-(2n+1)²*pi²*D*x/h²) ) where the SUM is the Sum operator with n=0 to n =xx (fixed value, tried it with 5). In order to fit the function, I programmed the following function: -------------------------------------- #pragma numlittype(push, TRUE) #pragma warning(error : 15618) #include <origin.h> // Add your special include files here. // For example, if you want to fit with functions from the NAG library, // add the header file for the NAG functions here. // Add code here for other Origin C functions that you want to define in this file, // and access in your fitting function. // You can access C functions defined in other files, if those files are loaded and compiled // in your workspace, and the functions have been prototyped in a header file that you have // included above. // You can access NLSF object methods and properties directly in your function code. // You should follow C-language syntax in defining your function. // For instance, if your parameter name is P1, you cannot use p1 in your function code. // When using fractions, remember that integer division such as 1/2 is equal to 0, and not 0.5 // Use 0.5 or 1/2.0 to get the correct value. // For more information and examples, please refer to the "User-Defined Fitting Function" // section of the Origin Help file. //---------------------------------------------------------- // void _nlsfSUM_Drying( // Fit Parameter(s): double D, // Independent Variable(s): double x, // Dependent Variable(s): double& y) { const double M=10410; const double h=0.0015; const double p=3.14159; const double n=5; // Beginning of editable part double bb = 0; for(int ii =1; ii<=n; ii++) { bb = (1/(2 * ii + 1)^2) * exp(- (2 * ii +1)^2 * p^2 * D * x / h^2 + bb); } y = M *(8/p^2)* bb; // End of editable part } ------------------------------------------------ however, fitting does not work and when I try out the function with a fixed value, the result is always 0. Is there someone who can help me fixing it and make it work? Thank you very much for your help. Best regards, Stefan [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.