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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 kemeyer[/i] [br]Origin Ver. and Service Release : 8.1 SR1 Operating System: Vista Hi, I am trying to define a fitting equation for some data I have. The equation I am trying to add is called the Sellmeier Equation, and the form of it that I wish to use is: n^2= A + B*Lambda^2/(Lambda^2-C) + D*Lambda^2/(Lambda^2-E) When I tried to define the equation using the fitting function organizer, I typed it in as: y = sqrt(A + B*Lambda^2/(Lambda^2-C) + D*Lambda^2/(Lambda^2-E)) and it compiled in the code builder. For the independent variables I put Y, for the dependent variables I put Lambda, and for the parameters I put A, B, C, D, E. When I ran the fitting function to fit my data, I didn't get a fit. It said that I need to initialize my variables, so I went back and under the parameter tab I entered values into the value boxes that would be close. Also, I checked the data delection under the settings tab to ensure it was using the data properly. I still can not get my function to work...could someone help me? This is the data I have... Lambda y 0.4046 2.0927 0.42 2.0794 0.44 2.0638 0.46 2.0506 0.48 2.0399 0.5 2.0305 0.52 2.0226 0.54 2.0159 0.56 2.0097 0.58 2.0046 0.6 2.0000 0.62 1.9959 0.64 1.9923 0.66 1.9889 0.68 1.9859 0.7 1.9832 0.75 1.9774 0.8 1.9727 0.85 1.9688 0.9 1.9655 0.95 1.9627 1 1.9603 1.05 1.9582 1.1 1.9565 1.15 1.9549 1.2 1.9534 1.25 1.952 1.3 1.9506 1.35 1.9493 1.4 1.9482 And these were the values for A, B, C, D,and E that were calculated by another method. A=2.3288, B=1.4519, C=0.048025, D=1.7045, E=158.08 Thanks, Katie [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.