I have a simulink model which uses inputs from 6 webcams for live video processing. For that I use 6 'From Video Device' blocks. The output from these blocks are processed upon to generate output in the form of (x,y) co-ordinates. All 6 webcam outputs are processed at a time in parallel. However matlab hangs and stops simulation if I use more than 3 webcams. I want to divide the 6 processing blocks among two processor cores using Parallel Computing Toolbox. But couldn't find suitable instructions anywhere for distributing a single simulink model among multiple processor cores. I am using Matlab R2011a.
Well, I cannot post my code or my model, but I can tell you what my model does. It takes input from 6 usb camera, tracks a moving object in each frame of each camera and gives me the location of the moving object in (x,y) co-ordinates. Thus, I get 6 (x,y) co-ordinates as output at a time. My model works well till I use 3 cameras and generate 3 (x,y) outputs. Adding fourth camera hangs the matlab and stops the simulation.
I'm afraid the reason you haven't found instructions for spreading a Simulink model across multiple cores is because these instructions do not currently exist (up to and including R2012b). The Parallel Computing Toolbox only allows you to conduct multiple, seperate simulations simultaneously across the different cores (i.e. to investigate the effects of parameter changes and such like).
For your application, you will likely be better off using Matlab "proper" and writing everything in m-functions and/or scripts. That way you will be able to leverage you multi-core processor by using commands such as parfor.
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What is the added value of simscape physical signals compared to normal simulink signals? As far as I can see, from a functional perspective there is no difference between the two types of signals: I can add units to both types, they both have a direction of flow, and they both have similar function blocks like adding, substracting... Only for physical signals the available types of blocks is very limited. Why didn't the matlab guys just use normal simulink lines instead of the physical signals?
Physical signals, unlike Simulink signals, have units associated with them. This means that they follow a number of rules, for example to ensure that the right unit is used (e.g. you can't add kg and m/s). From the documentation:
Using the Physical Signal Ports
The following rules apply to Physical Signal ports:
You can connect Physical Signal ports to other Physical Signal ports with regular connection lines, similar to Simulink signal
connections. These connection lines carry physical signals between
Simscape blocks.
You can connect Physical Signal ports to Simulink ports through special converter blocks. Use the Simulink-PS Converter block to
connect Simulink outports to Physical Signal inports. Use the
PS-Simulink Converter block to connect Physical Signal outports to
Simulink inports.
Physical Signals can have units associated with them. Simscape block dialogs let you specify the units along with the parameter
values, where appropriate. Use the converter blocks to associate units
with an input signal and to specify the desired output signal units.
Any sensor block in Simscape (in whatever physical domain) will output a physical signal. You can then convert it into a normal Simulink for feed to your controller. Similarly, any source block in Simscape (in whatever physical domain) will take a physical signal as input.
I suggest you just read the Simscape product page
In particular,
Simscape components represent physical elements, such as pumps, motors, and op-amps. Lines in your model that connect these components correspond to physical connections in the real system that transmit power.
Accompanying that description is the following image, which shows how Simscape models can be far more intuitive to build than a model which uses standard signal. This means models are far more maintainable and clearer to, for example, engineers who may not have a comp-sci background.
Let's delve into what a "physical connection" is somewhat.
[Simscape] employs the Physical Network approach, which differs from the standard Simulink modeling approach and is particularly suited to simulating systems that consist of real physical components.
[ ... ]
Each system is represented as consisting of functional elements that interact with each other by exchanging energy through their ports.
You stated in your question that both methods have a flow direction. This is wrong!
Simscape blocks try and balance the energy between the inlet(s) and outlet(s). For instance a fixed orifice in a fluid system may have high pressure on one side. Simscape will try and solve the pressure balance each iteration. You would need some custom Simulink subsystem to achieve this if not for Simscape.
What is the added value of simscape physical signals compared to normal simulink signals?
What is it that you think Simscape physical signals provide? Is it one number? How do you solve a mass-spring-damper system with just position? It's position AND it's speed AND it's acceleration.
I can add units to both types
No you can't. You put whatever you want in Simulink. You don't get to choose anything about what's in the physical signal in Simscape. You can specify units in the blocks that the signals connect, but you don't get to pick what the pipe itself is carrying.
they both have a direction of flow
No they don't. Your head and your torso are connected. There's no directionality to this. They're just connected. The physical signal is likewise just showing that (things) are physically connected. Again, the mass-spring-damper system: If the damper points to the mass, and the spring points to the mass, then is there any possibility that the damper could affect the spring? Yes, of course. The damper affects the spring because the damper affects the mass and the mass affects the spring.
The spring affects the mass, and the mass affects the spring. The signal is bidirectional. You're confusing signal directionality with kinematic chains.
they both have similar function blocks like adding, substracting
If you're on a train that's going 30 mph, and you're walking forward at 3 mph, how fast are you going relative to the world frame? What if you're walking backward? There is a physical meaning in adding and subtracting physical signals.
[For] physical signals the available types of [function blocks are] very limited
What is it that you're thinking they're missing? Can you also provide a description of what the physical meaning of that function block would be?
Why didn't the matlab guys just use normal simulink lines instead of the physical signals?
Because they're not the same. The biggest point is probably that Simscape is signal + derivative + second derivative, but again they're just conceptually different. Simulink is an easy way to write code - do this step, move along the arrow, do the next step, etc. Simscape is a pictorial representation of a physical system. The physical signal lines just show that things are connected. The system gets solved simultaneously.
I don't think it's mainly about the enforcement of physical signal units, nice though this is.
I think it's about the solver - and before it gets to the solver, about the choice of states and equation causality - rearranging the equations ready to be solved.
Simulink doesn't have any truck with this and just gets straight on with integrating signals as a succession of samples. I know it gets complicated with variable step solvers, but they are only doing extra fancy numerical analysis with the sampled data. Integration and the here-and-now is what it's all about!
Simscape just starts with a bucket of variables and a bucket of equations that variously depend on said variables. A 'bipartite graph', I believe they call it.
Just as we have to navigate a route through simultaneous equations to pick off the simple ones and substitute (or the matrix equivalents of this) Simscape has to do likewise in software so wants to keep alive augmented info on signals like which equations they are in and whether it knows or can easily obtain their derivatives, what they are, etc. Physical signals behave for us users just like Simulink signals, but I reckon they are there to provide the valuable service to Simscape of keeping this augmented info alive and linked between blocks so that one massive matrix equation can be formed for the whole system, not separate ones that get sampled as Simulink systems between Simulink blocks.
This rearrangement of equations ready for the more conventional solver getting stuck in is a black art indeed! We learn very little of how Simscape does it from the MathWorks docs, but you can install OpenModelica for free and see how that does it.
I have a laptop with a multi-core processor and I would like to run a lengthy loop in which Simulink simulations are performed. Is it beneficial to split the loop into two parts (it is possible in my case), open the Matlab application twice, and run a Matlab script in each of them?
Someone told me that Matlab/Simulink always uses one core per opened Matlab application. Is that correct?
MATLAB splits some builtin functions across multiple cores, but standard MATLAB code uses just one core. Generally, if you are running several independent iterations, then the computation time can benefit from parallelization. You can do this easily using either parfor (if the have the Parallel Computing Toolbox), or batch_job.
My MATLAB code uses the GPU to create raw data(25 seconds). Then in MATLAB, this raw data gets processed into scaler quantities that can be fed into an objective function(15 seconds).
Is it possible for a MATLAB particle swarm optimization code to start retrieving the next batch of raw data while the current raw data is processed?
Thank you.
You mean essentially work load distribution and timing. MatLab does have a ability to perform tasks in parallel by using SPMD:
http://www.mathworks.nl/help/distcomp/spmd.html
You might be able to first retrieve a set from your GPU and then start processing the data using MatLab AND retrieving the next set simultaneously using the SPMD statement.
I have a huge simulink model that takes about ~1 hour to execute. In my computer (HP Z210), the execution makes the computer use all cpu cores at 100%. What is intriguing me is that the same model running on my colleague computer (Dell precision T3600) uses ~50% of the cpu "power" (some cores at 100% and some cores remain idle).
My questions is:
I always thought Simulink runs in a single core. I´m not using parrallel computer toolbox or any other toolbox. I´m only using Matlab and Simulink licenses.
Why the execution in my computer is different from my colleague? Does it have anything to do with hyper-threading?
While simulink itself is single threaded in executing a single model, a block itself might be multi threaded. For example a simulink block executing matrix multiplication will use the multi threaded implementation which is also used by matlab.
Simnulink is definitely a single-threaded application. The exception to this is if you are using Rapid Accelerator mode and have multiple cores available, then the standalone executable runs on a separate core. See How Acceleration Modes Work for more details.
If you are running multiple simulations, then you can distribute these across multiple cores with the Parallel Computing Toolbox, or even multiple workers (machines) with the MATLAB Distributed Computing Server. However, this is for multiple simulations of a model (e.g. a Monte-Carlo simulation), not for breaking uo a large model in several chunks (currently not possible as far as I know). see Run Parallel Simulations for more details.
Not sure why the execution would be different from one machine to the other. Are you both using the same release of MATLAB? Same O/S? There are so many things that could be different. With regards to speeding up the execution of model, you could try running the model in accelerated mode, using the Simulink profiler to see where the bottlenecks are, changing some of the solver settings (e.g. variable-step vs fixed-step), etc...
If your model can be built with Simulink Coder, you can use xMOD software (www.xmodsoftware.com) to execute your model in multi-core (subsystem per thread basis, with a dedicated solver and step-size for each subsystem).
I am analyzing EMG data in my research lab. One of the steps is to calculate a continuous wavelet transformation of the dataset (size ~80000). Therefore, I use Matlab with the wavelet toolbox and "cwt" to plot a 3D-scalogram.
The calculation takes a lot of time and any interaction like 3D-rotation (which is very important to see different aspects of the data) is nearly impossible.
The resource-monitor shows that only one of my hexa-core processor is working. I use parallel computing for other calculations and haven't found any solution or even a similiar question like this.
Is there anything I can do to activate multicore support for plots?
I'll hazard an educated guess and plump for the answer No to your question Is there anything I can do to activate multicore support for plots?
Matlab can certainly use multiple cores for its computations. Many of its intrinsic functions are already multi-threaded and will use any available cores without the programmer (or user) having to do take any special measures. For your own computations you can use the Parallel Compute Toolbox.
However, unless you have some very special graphics hardware (and if you do why didn't you mention it ?) your display shows you why only one processor is being used when you interact with your 3D plots -- somewhere between the screen and the hardware of your computer there is a bottleneck through which the outputs of all those cores are squeezed into one stream of bits and bytes for presentation.
Your experience is consistent with that bottleneck being the Matlab visualisation routines, I think it is safe to conclude from the evidence you present, that the Mathworks haven't multi-threaded the routines which compute the new screen positions of each element in a plot as you rotate it, or any of the other processing that goes on to turn the results of your analyses into a picture or pictures. If they did parallelise those routines, that would shift the bottleneck but not remove it.
To remove the bottleneck you would have to have a way for different Matlab threads to separately address different parts of your screen; I see no evidence that Matlab has that capability. Google will find you a ton of references to parallel rendering but I see no sign that Matlab currently implements any aspect of this.
I'll just add, in response to your comment where you write unfortunately I can't resample my data that you should be mindful that Matlab's visualisation routines are resampling your data for presentation unless you are only visualising datasets with numbers of samples less than the number of pixels available. If you visualise a time series with 80000 samples on a display with 2000 pixels horizontally, something has got to give.
You might get better graphics performance and superior understanding if you take charge of that resampling yourself.
Matlab plotting performance is pretty bad, it's more focused on customizability than performance. Using MEX to run some native C++ code to plot the data with OpenGL will likely be much much faster.