I have 2 sets of data: x and y, and 2 nonlinear functions x(t) and y(t).
x(t) has 3 parameters: a,b and c;
y(t) has 6 parameters: a,b, c (shared with x(t)) ,d,e and f.
How can I simultaneously fit x(t) with x and y(t) with y in such a way that the values obtained for the shared parameters (a,b and c) are the ones that best fit both x and y? And if it is possible to do that, can I also get the values for the sum of chi-squared?
If this cannot be done, is there any way to fit complex numbers with complex functions?
Because I could write my data as x+i*y and fit it with a function x(t)+i*y(t). Would it work?