The getfield function can be used to access a field in a structure, a fints object, or a vrnode object. If data is a structure, the code
d = getfield(data,'data');
is accessing the value of the field 'data' in the structure data, and is equivalent to doing
d = data.data;
This is what getfield does under the hood for a structure.
Is this what you are trying to do? What is the exact error message you are getting? You can check that data is a structure by typing class(data) in the MATLAB Command Window. You can also check that data has a field named 'data' by typing fieldnames(data) in the Command Window.
