1. The problem statement, all variables and given/known data Determine the values of Sellmeier's coefficients (S and λ0) using the least-squares method and Sellmeier's dispersion equation: n2=1+Sλ2/(λ2-λ02) 2. Relevant equations n2=1+Sλ2/(λ2-λ02) 3. The attempt at a solution I understand how to use the least-squares method with a simple equation like y=mx+b (see below), but when trying to do the same thing with Sellmeier's equation, I get confused with where to put the summation symbols. Also, I am not sure if I use the squared version of Sellmeier's equation or to take the square root of it. With y=mx+b, I know to take a y' point on the line corresponding to one of the points. A general equation would be achieved, i.e. Di=yi-y'i --> Di=yi-mxi+b. You would then square the equation, take the summation of it, and then the derivatives with respect to m and b to minimize, setting both equations equal to 0: (1) Ʃ(yixi)-mƩ(xi2)-bƩ(xi)=0 (2) Ʃ(yi)-mƩ(xi)-bn=0, n is the number of data points The solved linear equations yielded: m=[Ʃ(xi)][Ʃ(yi)]-nƩ(yixi)/[[Ʃ(xi)]2-nƩ(xi2)] b=[Ʃ(yixi)][Ʃ(xi)]-[Ʃ(xi2)][Ʃ(yi)]/[[Ʃ(xi)]2-nƩ(xi2)] With Sellmeier's however, I am achieving some complex starting equations. Is there some mathematical "trick" I don't know about? Thanks for any help!