How to fit two graph synchronous

I have two graphs, and will be fit by two corresponding functions. Since these two functions have a same paramenter, I need to fit these two graph synchronous. anyone
can give me a hint how to do it. Thanks.

Hi Haipeng,

Add your graphs to a TMultiGraph object and use the
TMultiGraph::Fit routine :

There is an example in tutorials/fit/fitMultiGraph.C