Hello, I am new to GSL and new to nonlinear fit as well. I would like to use the nonlinear fit of GSL, could you please help?
I have a data set as follows: x f(x) 800 0.0290073021087 750 0.0555646715288 700 0.106436396964 650 0.203883264078 600 0.390546716694 550 0.748108181465 500 1.43303176612 450 2.74503085727 400 5.258218684 350 10.0723325771 300 19.2939642948 250 36.9583763602 200 70.7952788921 150 135.611247219 100 259.768880922 50 497.597897513 0 953.169089118 and I would like to fit this data set with an exponential function: y = f(x) = a * exp(-b*x) + c. I installed GSL 1.11-2 on my Ubuntu 8.10. I am able to run the example from http://www.gnu.org/software/gsl/manual/html_node/Example-programs-for-Nonlinear-Least_002dSquares-Fitting.html in my Eclipse. I compile, run and see the results. However, i check the example and i see that it only allows me to input y (or f(x)) and this example assumes that x increases from 0 to 39 (in method expb_df (const gsl_vector * x, void *data, gsl_matrix * J)). I tried to change the for loops in file expfit.c to represent my x values (from 0 to 800) and input y in the main file with my y values but the program output no fit values at all. Also, in the example, there are guessed values for the parameters A, lambda, b. What if we do not know the guessed values and we input an arbitrary guessed values? Like in this case, I do not know the guessed values of the parameters A, lambda, b. How could I find the best fit? I guess my fitting task is very simple (fit the above data set) compared to the risk set of functionalities GSL can provide. So, there might be some simple way for me to use GSL and fit my data set. Could you please help? Thank you very much, -Long _______________________________________________ Help-gsl mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-gsl
