{"id":13239,"date":"2022-11-20T11:36:39","date_gmt":"2022-11-20T16:36:39","guid":{"rendered":"https:\/\/blogs.mathworks.com\/simulink\/?p=13239"},"modified":"2022-11-20T11:36:39","modified_gmt":"2022-11-20T16:36:39","slug":"parallel-simulations-your-options-to-configure-data-when-using-parsim-and-batchsim","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/simulink\/2022\/11\/20\/parallel-simulations-your-options-to-configure-data-when-using-parsim-and-batchsim\/","title":{"rendered":"Parallel Simulations: Your options to configure data when using parsim and batchsim"},"content":{"rendered":"
Today I am happy to welcome guest blogger <\/span>Reid Spence<\/span><\/a>. Reid helps Simulink users running simulations in parallel using functions like <\/span>parsim<\/span><\/a> or <\/span>batchsim<\/span><\/a>. In this post, he shares best practices to manage the data needed by Simulink models in the context of parallel simulations.<\/span><\/div>
You can download the examples used in this blog post <\/span>here<\/span><\/a>.<\/span><\/div>

The Problem<\/span><\/h2>
Did you ever run into a situation where you have a model that simulates successfully when using the <\/span>sim<\/span><\/a> command or the play button, but errors out when simulated using <\/span>parsim<\/span><\/a> and the <\/span>Parallel Computing Toolbox<\/span><\/a>? This can happen for various reasons, let's begin with the one I see the most often.<\/span><\/div>
Let's start with this simple model, which uses 3 variables defined in the MATLAB base workspace: <\/span>k<\/span>, <\/span>c<\/span>, and <\/span>m<\/span>:<\/span><\/div>
\"\"<\/img><\/div>
I can successfully simulate this model:<\/span><\/div>
k=5; c=3; m=2;<\/span><\/span><\/div><\/div>
mdl = <\/span>'simpleSuspension'<\/span>;<\/span><\/span><\/div><\/div>
in(1:2) = Simulink.SimulationInput(mdl);<\/span><\/span><\/div><\/div>
in(1) = in(1).setVariable(<\/span>'k'<\/span>,10);<\/span><\/span><\/div><\/div>
in(2) = in(2).setVariable(<\/span>'k'<\/span>,20);<\/span><\/span><\/div><\/div>
out = sim(in,<\/span>'ShowProgress'<\/span>,<\/span>'off'<\/span>);<\/span><\/span><\/div><\/div>
figure;<\/span><\/span><\/div><\/div>
plot(out(1).logsout.get(<\/span>'x'<\/span>).Values); hold <\/span>on<\/span><\/span><\/div><\/div>
plot(out(2).logsout.get(<\/span>'x'<\/span>).Values);<\/span><\/span><\/div>
<\/div>
<\/div>
<\/div>
<\/div><\/div><\/div><\/div><\/div>
Now, let's try to use <\/span>parsim<\/span> to simulate the model in parallel with different values of <\/span>k<\/span>:<\/span><\/div>
mdl = <\/span>'simpleSuspension'<\/span>;<\/span><\/span><\/div><\/div>
in(1:2) = Simulink.SimulationInput(mdl);<\/span><\/span><\/div><\/div>
in(1) = in(1).setVariable(<\/span>'k'<\/span>,10);<\/span><\/span><\/div><\/div>
in(2) = in(2).setVariable(<\/span>'k'<\/span>,20);<\/span><\/span><\/div><\/div>
out = parsim(in,<\/span>'ShowProgress'<\/span>,<\/span>'on'<\/span>,<\/span>'ShowSimulationManager'<\/span>,<\/span>'on'<\/span>);<\/span><\/span><\/div>
[20-Nov-2022 11:25:57] Checking for availability of parallel pool...\r\nStarting parallel pool (parpool) using the 'Processes' profile ...\r\nConnected to the parallel pool (number of workers: 2).\r\n[20-Nov-2022 11:26:19] Starting Simulink on parallel workers...\r\n[20-Nov-2022 11:26:26] Configuring simulation cache folder on parallel workers...\r\n[20-Nov-2022 11:26:27] Loading model on parallel workers...\r\n[20-Nov-2022 11:26:32] Running simulations...<\/div><\/div>
Warning: One or more simulations completed with errors. For more information, inspect the SimulationOutput objects at these indices:
[1 2]<\/div>
<\/div><\/div><\/div>
[20-Nov-2022 11:26:34] Cleaning up parallel workers...<\/div><\/div>
Warning: Error in the simulation was caused by missing variable 'm'. Set \"TransferBaseWorkspaceVariables\" option to \"on\" to fix the issue.<\/div>
<\/div><\/div><\/div><\/div><\/div><\/div>
As you can see, the simulations errored out. We can look at the <\/span>Simulation Manager<\/span><\/a> to learn more on the error.<\/span><\/div>
\"\"<\/img><\/div>

What Happened?<\/span><\/h2>
Let's look in details at what happened. For that, we can look at the progress displayed by <\/span>parsim<\/span>. The first thing we see is that <\/span>parsim<\/span> starts a parallel pool.<\/span><\/div>
[08-Nov-2022 14:11:17] Checking for availability of parallel pool...<\/span><\/span><\/div>
Starting parallel pool (parpool) using the 'Processes' profile ...<\/span><\/span><\/div>
Connected to the parallel pool (number of workers: 2).<\/span><\/span><\/div><\/div>
Starting a parallel pool means the MATLAB session you are interacting with (the <\/span>Client<\/span> in the next image) is launching new MATLAB sessions in the background, without the user interface (the <\/span>Workers<\/span> in the next image)<\/span><\/div>
\"\"<\/img><\/div>
Once the parallel workers are up and running, we start Simulink on each worker:<\/span><\/div>
[08-Nov-2022 14:11:39] Starting Simulink on parallel workers...<\/span><\/span><\/div><\/div>
To avoid conflicts between workers, we configure each of them to use a different cache folder:<\/span><\/div>
[08-Nov-2022 14:11:46] Configuring simulation cache folder on parallel workers...<\/span><\/span><\/div><\/div>
The model is loaded on each worker:<\/span><\/div>
[08-Nov-2022 14:11:47] Loading model on parallel workers...<\/span><\/span><\/div><\/div>
Finally, the model is being simulated:<\/span><\/div>
[08-Nov-2022 14:11:52] Running simulations...<\/span><\/span><\/div><\/div>
Hopefully, you see where I am going with that... <\/span>the parallel workers need to be configured!<\/span> In the above example, \"be configured\" means loading variables in the base workspace. If you are dealing with large complex models, you probably understand that \"be configured\" can mean a lot of things. <\/span><\/div>
What we will discuss in this post are the different options offered by <\/span>parsim<\/span> and <\/span>batchsim<\/span> to automate the configuration of the parallel workers<\/span><\/div>

Multiple Options to Configure Parallel Workers<\/span><\/h2>
Articles have been published on this blog on the topic of parallel simulations:<\/span><\/div>