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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 peter.cook[/i] [br]Hi, I'm trying the effect of different tolerance criteria and derivstep values to obtain global minima (least squares). Generally, lower tolerance criteria give at least as good a fit as expected. Very occasionally setting to a lower tolerance gives a slightly worse fit. In these cases a lower nlsf.derivstep value helps. My question is what range of values is reasonable and what exactly are the implications of lowering the nlsf.derivstep value? The help gives 'A smaller value gives higher precision but may cause numeric round-off errors. The default value is 0.005.' Where does these round-off errors occur? What does the higher precision refer to? Cheers, pete [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.