The IMSL routine DRONE is used for the linear least squares fit and for the fit through the origin ; DRPOLY is used for the polynomial fits ; and DRNLIN is used for the nonlinear fits . The equation of the fit, the correlation coefficient, the mean square residual over the variance, the variance, and the number of points in the fit are shown. The ANOVA table is available by entering A before a linear or polynomial fit.
After selecting the nonlinear fit (with N) you will be prompted for an expression and estimates for the coefficients. For example, suppose you have just plotted TAUP vs TE and you want to fit it to a exp-Te/b + c Te, you would enter the expression a1*exp(-x/a2)+a3*x. A1, a2, and a3 are the coefficients for which you will be prompted for estimates, and x refers to your x axis parameter or expression, TE. Note: Use x in the fit expression as shown, not your x expression! You can have up to 9 coefficients. The nonlinear option can also be used to draw an arbitrary function of x if you don't give any coefficients.
If you have specified an error parameter for y then the estimate of the error will be used in the fit. The linear and polynomial fits are given for logarithmic axes as well as linear. You can write the coefficients of a fit as well as the associated statistics to a file. Prior to the graph, select the write coefficients option from the OUTPUT submenu of PLOT.