How to use parpool for independent expressions

How to evaluate independent expressions in local parpool on laptop.

When I try the code below, the parpool is idle.

How to force matlab to evaluate the expressions in parallel.

x = 1; y =2; z=3;
parpool('local',4)   
s = x + y + z; 
a = 2*x + z; 
w = 3*y + 2*z;  
f = 3*x + 2*z;  

[Raymond Norris]

Let me ask you this. Using a pool of workers (i.e. processes) cancels out any implicit threadedness. So will there be any value in doing as your requesting?

To see the impact, try the following:

maxNumCompThreads(1);
tic
< run code >
toc
maxNumCompThreads('auto');
tic
< run code >
toc

Next, run your code using a parallel pool of workers and parfeval (as Mohammad has suggested) and see how close it gets to your timings with maxNumCompThreads set to 'auto'. You might see it's a wash.

Answer 1

[Mohammad Sami]

You can use the parfeval function to make these calculations on a worker thread.

x = 1; y =2; z=3;
p=parpool('local',4)   
Fs = parfeval(p,@(x,y,z) x + y + z,1,x,y,z); 
Fa = parfeval(p,@(x,z)2*x + z,1,x,z);
Fw = parfeval(p,@(y,z)3*y + 2*z,1,y,z);  
Ff = parfeval(p,@(x,z)3*x + 2*z,1,x,z);
s = Fs.fetchOutputs;
a = Fa.fetchOutputs;
w = Fw.fetchOutputs;
f = Ff.fetchOutputs;

To avoid copying of data to workers from main thread if you have large datasets, you can use thread based parpool.