Do you need a symbolic equation? It is rather difficult to get one.
I suppose, there are two ways:
- Polynomial function. Read the doc for polyfit
- Sum of ration of polynomial functions. Read the doc for rationalfit
The first option can be (and I suppose will be) not accurate, because it is just one polynomial. So I don't reccomend it.
The second one can fit almost any data, but in my opinion it is more difficult to use. I can't give an example, because I only know the theory behind, but have never implemented it in matlab yet.