Question

I’m wondering how I can copy (and maybe delete) handle objects within MATLAB.

I am currently coding a solver for large systems of equations using MATLAB and an add-on called CPLEX. This solver essentially involves creating CPLEX handle objects and then solving them using a solve method as follows:

P = Cplex() %Create a Cplex object
%Code to specify the Cplex parameters
P.solve() %solve the Cplex object

In the code above, P is a MATLAB Handle Object that belongs to the Cplex() class. It stores a structure of matrices that relate to the factors of their equations.

The main issue that I am running is that I have to “solve” the same CPLEX object numerous times and I would like to do this in parallel, using a parfor loop. Unfortunately, the parfor loop in MATLAB requires transparency, since multiple threads cannot work on the same object.

I’ve thought of several ways around this: previously, I created and setup the Cplex() file within the parfor loop (this turns out to be slower than a single thread implementation); I also tried saving the object to disk and loading it up within the parfor loop (again too slow). Now I’d like to see if I could copy the object (either within the parfor loop, or outside of it). Unfortunately, however, there is no built-in “copy” function for Cplex objects and I would have to code something like that myself.

Essentially what I would like to do boils down to:

P = Cplex() %creates Cplex object
%Setup Cplex object

Q = cell(1,n) %create a container for Cplex objects

parfor 1:n

Q{i} = P.copy %create a copy of P and label it as Q{i}
Q{i}.solve()
Q{i} = [] %delete Cplex object (for memory purposes /preferable, but not necessary)

end

Answer 1

I don’t have CPLEX and since I cannot replicate your code, please try the following suggestion and let me know if it works (or if you get an error, what the error is).

Try defining Q outside of the parfor loop as

Q=arrayfun(@(x)P.copy,1:n,'UniformOutput',false);

This should create a cell as you had earlier and you can access it as Q{i} and should save you some time (because if you’re worried about memory issues that you delete each element after processing, then copying it might involve some time overhead too).