Data fitting using implicit functions and infinite series

How to use this equation for data fitting？

J/J∞ is dependent variable，t is independent variable，L, DL is constant，and k is parameters to be fitted.

Answer 1

[Torsten]

Depending on the number of series terms you want to use in the evaluation of J, determine the roots of the nonlinear equation tan(...) = ... (e.g. using "fzero" several times).

Then use the k-value from the solver (e.g. lsqcurvefit) to evaluate the series at your measurement data vector t and return the calculated values for J (or J/J_inf) to the solver.