To get data out of a parfor loop, you must have either a "sliced output" or a "reduction output". Your code example above has neither of these - v1 and v2 will be analysed as "temporary variables" because you assign a whole new value to them in each iteration of the loop.
I spotted your other question about handle classes in parfor. It's not clear to me which part of your algorithm is the time-consuming piece that you are hoping to speed up with parfor. But in general, you cannot modify instances of handle classes on the worker and have the changes show up back at the client (nor on other workers). So, in general, modifying a graph structure in this way is really not amenable to parallelism.
My general advice would be: use the MATLAB profiler on your code running in serial, and work out where the real time is being spent. See if you can arrange things so that this is divided up into independent pieces of work. That is the simplest way to being able to run stuff in parallel.
