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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 neutrondude[/i] [br]Origin Ver. and Service Release (Select Help-->About Origin): 7.5 Operating System: XP2 prof Hi, I have a rather strange problem. I need to make an integral over a rather stiff funcyion of a parameter, lets say, x. Its on the form: y = int exp (exp(-arg(x))dx Strangly Origin is not able to find the minima using the Marquard-Lewenberg routine but using Simplex it does. That might be related to the problem with calculations of the the derivatives and steep minima. So far I can accept this- but the problem is that when I calculate/generate the function after seeing that the fited line coinicides withe the exp data, the calculated curves is completely off. In other words the fitted line is OK, but saying "Done" the curve turns completely different!! I have used a simple summation to calculate the integral, but varying the step, range do not influence anything. (By the way where are the descriptions on how to use the NAG routines to do various integrals?) Can you please helpe me? thanks a lot in advance. [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.