All Forums  Origin Forum  Origin Forum  Nonlinear curve fit: parameters do not vary

Note: You must be registered in order to post a reply.
To register, click here. Registration is FREE!

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 studentAgain[/i] [br]Origin Ver. and Service Release (Select Help-->About Origin): Operating System: OriginPro 8.1 SR3, Windows 8.1 Hello, I have a quick question about the nonlinear curve fitting. When I try to fit my data with for instance, Polynomial cubic function y = A + B*x + C*x^2 + D*x^3 everything works great when I use automatic parameter initialization, however; as soon as I try to change slightly any of the parameters manually (i.e by typing its value in the parameter box) the fit becomes poor and does not converge any more. I click "fit until converged" button but nothing happens (it shows a message: "cannot find direction to change parameters to reduce Chi-sqr"), the parameter that I just manually entered appears to be frozen/fixed and does not change anymore. I do not understand why and would really appreciate any help. Thank you, [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.