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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 merrick[/i] [br]I'm trying to created a new (user-defined) Non-Linear Curve Fit function to fit my experimental values based on the exchange equations by Johnson. I simulated in excel (using solver and an approximation) and got a good agreement, however as soon as i used this simulated values in origin the fir goes completely crazy. There is no compilation error, so I assume the user-defined function is working well. Can anyone help me? My origin code is: ouble pb,kb,s,l,z,Ma,Mb; pb=1-pa; kb=ka*pa/(1-pa); s=0,5*(ka+kb+Da*x+Db*x); l=0,5*(ka-kb+Da*x-Db*x); z=sqrt((l^2)+ka*kb); Ma=(0,5*pa-((l*pa-kb*pb)/(2*z)))*exp((-s+z)*T)+(0,5*pa+((l*pa-kb*pb)/(2*z)))*exp((-s-z)*T); Mb=(0,5*pb+((l*pb-ka*pa)/(2*z)))*exp((-s+z)*T)+(0,5*pb-((l*pb-ka*pa)/(2*z)))*exp((-s-z)*T); y=Ma+Mb Thanks [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.