Welcome to the MATLAB Central Simulink blog! The purpose of this blog is twofold: First, I want to share Simulink tips and tricks that I've learned over the years. At the same time, I hope to learn from you about your experiences with Simulink. Where is it good? How can we improve it?
I've been using Simulink for 9 years, first as a member of our technical support team, and then as a trainer. I still remember when I first learned about the power of Simulink as a newly hired support engineer back in 1998. During a training class I saw differential equations drawn on a whiteboard and then simulated with a few clicks of the mouse. I got excited by how clearly it all worked. Simulink provided me with a framework for thinking about systems and the relationships between their basic components.
Of course, Simulink is much more than a simple tool for solving differential equations. It has a richness and depth that will give me plenty of material to draw on. What kind of topics can you expect to read about here? We'll talk about applications of Simulink in controls, signal processing and communications system design. With your help, we'll talk about how Simulink is used in areas I don't even know about yet. We'll talk about Model-Based Design in general, and we'll get a peek at some of the internal machinery of Simulink. I look forward to posts about all of these:
- solvers
- sample times
- modeling
- hacks
- blocks
- model reference
- libraries
- masking
- custom code
An example: batch simulation
Let me start off with a specific example about running simulations. Simulink models are built using block diagrams, and once they've been created most everyone runs them by clicking the run button on the toolbar.
If you have to run a sweep of parameters you might change the parameter and then click run, change it again and click run. But if you have to run hundreds or thousands of simulations while modifying a parameter you will want to write a script for batch simulation. You can run simulations directly from MATLAB with the sim command like so.
>> [t,x,y] = sim(sys);
This returns the root level outputs (y) and the internal states of the model (x) at each recorded time step (t). A batch script might look like this:
open_system('vdp_mu') muSweep = .5:.1:1.5; for i = 1:length(muSweep) mu = muSweep(i); [t,x,y] = sim('vdp_mu'); plot(t,y); hold on; end title('VDP States for mu=.5 to 1.5') xlabel('Time'); legend('x1','x2')
If you are already familiar with the sim command, then you probably know that some times you are only interested in the outputs (y) of the model, and not the states (x). For large models, or long simulations, those state variable outputs could be a waste of valuable memory. Using simset you can provide additional options to the sim command to specify that you only want time (t) and outputs (y). The state variable returned from sim will be empty.
[t,x,y] = sim('vdp_mu',[],simset('OutputVariables','ty')); whos t x y
Name Size Bytes Class Attributes t 206x1 1648 double x 0x0 0 double y 206x2 3296 double
You can learn more about sim and simset in the Simulink documentation.
What do you think?
That's your first Simulink tip. Now it's your turn. What do you like about Simulink? What would you like to talk about in future posts? Please leave a comment below. I have learned from Doug that t-shirts get comments on your blog, so I'll be randomly selecting five commenters on this post to receive a MathWorks t-shirt!
Get
the MATLAB code
Published with MATLAB® 7.5
Hey Seth, congratulations on the new blog! Took a while to get the first one published ;)
For people unfamiliar with the interaction of Simulink and workspace variables, could you discuss how changing the variable ‘mu’ in the base MATLAB workspace ends up affecting the simulation?
A convention that Loren uses that I appreciate is to hyperlink the first mention of any new function to its online documentation. I nearly missed the link to SIM and SIMSET because it was located a long ways after you started talking about the functions.
Cheers,
Eric
Eric S - Thanks for being my first commenter! That is a great suggestion. For those of you who don’t know, workspace variables can be used as the parameters in your blocks. In my example, the gain block used the workspace variable mu.
The batch script assigns a new value to mu before calling sim, and on each iteration of the loop the simulation picked up the latest value.
Seth, welcome to the “blog-o-sphere”! Excellent first post, and great use of publish.
Hey seth, you welcome too and thanks for the blog on Simulink. Believe me it is a smart move. I was wondering why there is no such things in the mathworks site. well I will be proud to wear the mathworks t-shirt in class with Simulink engraved at the lower side. Once more good job and keep it up.
Kwadwo D - Thanks for your support. Many people have asked for a Simulink blog over the years, and I am happy to be writing it.
I almost always use SIM to run Simulink. In addition, I almost always call SIM from a function, so I have to use the ‘SrcWorkspace’ option every time as my model parameters are in the current workspace. As it is, SIM is peculiar in that it looks like a function, but it doesn’t behave in the same way and maybe there should be a version which runs in its own workspace with input and output variables passed as fields in structures.
James M - Your comment is a very important one. The interaction between Simulink and the workspace can be tricky one to manage if you run your model from inside functions. I ran into this exact problem while writing a function for benchmarking model performance. SrcWorkspace and DstWorkspace are a topic I will talk about in the near future.
Hi Seth,
I have just learned Simulink for two months and before I was alsways Matlab user. Recently I try to place my algorithm written in Matlab into Simulink because of its beautiful and clear organisation of blocks. Also it provides me a better examination of the interface signals and the real-time ability of the algorithm. I am very excited about Simulink and also your new Blog, and hopefully it will also be useful like other Blogs in Matlab websites (like it from Doug) ^^
best wishes
song
Song - I agree that Simulink diagrams provide a beautiful way to express your algorithm, and you get the added benefit of seeing the data flow in your model. Did you see Doug’s latest video post plugging this blog? Thanks for the comment.
Great to see a blog dedicated to simulink! Greaet first post. Keep it up!
> What would you like to talk about in future posts?
I would be very interested in some more advanced stuff such as automatic code generation, fixed-point modelling, the handling of very large model hierarchies, model-driven testing, and the use of modeling patterns.
Tom – The topics you have suggested are great ones indeed. Thanks for the ideas. Stay tuned.
I’d like to read advanced topics such as: code generation, linking Simulink and other tools, advanced programming for Simulink. Also, I’d like to hear about experience in dealing with errors (for example the annoying algebraic loop error).
Truong N – Thanks for bringing up the subject of algebraic loops. There are some very interesting things to be said about how Simulink works with algebraic loops and what it means if your system has them.
I use Simulink + xPC for robot control. It would be great if you can cover the issue of handling multiple sampling rates in a single system. I’ve used Unit Delay, Rate Transition and etc. , but the inner workings are not quite clear to me, and sometimes I don’t understand the error messages.
Daisuke – Sample times and multi-tasking real time execution are great topics to talk about. I recommend the Real-Time Workshop documentation on Models with Multiple Sample Rates for an overview. Thanks for the ideas.
I’d like to see a post on the differences between embedded MATLAB and regular MATLAB coding, as well as the limitations on embedded code.
Daniel C – Thanks for the topic idea. Loren touched on this topic briefly last year in this post. Maybe I can team up with her to write about Embedded MATLAB.
I’d second the calls for advanced Simulink topics. I’ve always preferred the advanced Matlab topics on Doug’s blog.
The demos that ship in the help are great for the basics. The blog lets me see some advanced topics and then read comments from other users about how they’ve found even better ways to do it.
Bob – You have brought up a valuable point about reading the comments of other users. We (the Simulink community) can all learn from each other about how to best use these tools for our work. I look forward to your continued contribution to the discussion.
At last! simulink. i have some time using this environment, i’m student of electrical engeenering and i discovered that simulation made under simulink are more fast than those using matlab function like ode45(). Even more, we can use vector and all your brief sintaxis.
thanks
Christian – Great observation about performance. Have you ever tried Accelerator mode or Rapid Accelerator mode in your Simulink model? That can make your simulation run even faster! Those modes became part of core Simulink in R2007b.
Hi Seth,
Congratulations and thanks for new blog on Simulink topics. I would also like to see the advanced topics on code generation. And some info if Simulink can be used in conjunction with AccelDSP synthesizer.
thanks,
Raj – I am sensing a lot of interest in code generation. Thanks for your ideas. I’ll have to get some help to talk about AccelDSP synthesizer.
Interesting option Accelerator mode or Rapid Accelerator mode. i will try to use them, because sometimes i work with system that take a long time of simulation, because have signals highly abrupt, for example a PWM signal, or another type of modulated signal.
Seth,
Can you help me with if-then statements, I want to use a pulse generator to determine if data is to be passed along. In the basic case, I want half of the data passed along and the rest stopped, but I seem to always get zeros instead of empty cells. Is there another way of solving this. I’ve tried multiplying by an empty cell and switching to an empty input but no joy. Any suggestions?
I’m here only for the t-shirt :) (Just Kidding)
When I do controller design I use Simulink but most of the times I just use plain Matlab. What I’d like to see in a Simulink blog is, how I should connect Simulink and LabVIEW, I’ve been always wondering if there is a legitimate way of doing this
Jeremy - I’m not sure I know what you mean when you say “multiplying by an empty cell”. The if-then-else construct usually takes the outputs from the conditionally executed systems and merges them. Have you tried using a merge block?
Switching is another alternative, but in that case, the logic should feed the control port on the switch.
Sia - Can you elaborate on what you mean by “connect Simulink and LabVIEW”? Are you trying to access data from instruments or acquisition hardware?
hi there,
glad to see that a simulink related blog is up and running. would this be a forum to ask specific simulink questions? i am having difficulties with a costas loop i am working on.
thanks
-t
Seth,
What I am trying to do is have a simulation running for 10 seconds and get 5 seconds worth of data plotted, sampled from every second point. I don’t want every second value to be zero. Thus if I attach a scope to the input it will have 10 seconds woth of data, but a scope attached to the output of the sampled data will have only 5 seconds worth of data on it. A decimate vector applcation would do it for me, but simulink seems to combine data well, but not strip data.
Cheers,
Jermy
@Tami - You have found a good place to ask questions, but I have to warn you that I might not have the answers. :-)
You may want to post on CSSM, or if it is a technical support question create a service request.
@Jeremy - If you are looking at the data, set your scope parameters so the Sampling Decimation is 2. Then you can just look at the decimated data.
If you are trying to log data like that, try the To Workspace block. It also has a decimation parameter. The other option is to change the sample time by 2. For this, a Rate Transition block might be your best bet.
Waoouh the SL Seth Blog is alive!!!
Congratulations Seth!
It was time to have a Simulink blog.
As a moderator on the French MATLAB Central:, I have already promoted your blog.
You cAn find my post:
http://www.developpez.net/forums/showthread.php?t=500449
and the francophone MATLAB Central:
http://www.developpez.net/forums/forumdisplay.php?f=148
I am looking forward to reading your next post soon!
Aurélien
Seth –
This blog is a great idea, and the first article is right on target. Congratulations! I am looking forward to your future posts.
– Rick
Seth,
1. This is a matlab comment. The two lines
for i = 1:length(muSweep)
mu = muSweep(i);
could be simply,
for mu = muSweep
2. Simulink is diagram focused. How do others insert graph in comment (as you did in #32)?
Great start!
Seth,
I have a signal generator creating a data stream. I want to average two or three of the values of the data stream at a time, and hence reduce the size of the data stream. The classic way of incrementing a counter and an if-then statement doesn’t work unless I can get access to the system clock. Is there another way that Simulink can average data, rather than decimation and losing the data?
Thanks,
Jeremy
@Wei - Thanks for pointing out that MATLAB Tip. Doug and Loren will be pleased that we can learn MATLAB while reading a Simulink blog.
If you would like to include HTML in your comments, you may, however some types of markup may be held for moderation, and it will not display immediately. You could also e-mail me with the images you would included in your comment, and I can add them later.
@Jeremy - Could you write out the expression for the type of averaging you are doing? Do you mean something like this:
Y(n) = (U(n-2)+U(n-1)+U(n))/3
Seth,
That would work, but while doing this I would like to reduce the number of data points in the output stream by the denominator value.
- Jeremy
@Jeremy - This can be done using a ZOH rate transition from the fast to slow rate. You will need to set the output sample time of the Rate Transition block to the slower rate, and that will reduce the number of points.
To achieve this, I set the FIR Filter block with numerator of [1 1 1]/3. Try it out and let us know how it works.
Seth,
Thanks for that it works fine with a divide by 3 at the end. Other questions, is it possible to append to a file rather than write over a file with the same variable? How do I guarantee tasks are completed sequentially, do I need to put a counter through subsystems?
- Jeremy
Dear Seth,
I want to measure the power factor of a boost converter in the simulink, which equipment in the library I can use?
Your blog is great, I’ll come many time.
Hi Seth, I’ve a little question about ToWorkspace blocs :
Is it possible to create variable name including an index ?
Like : [ varName num2str(i) ]
So I can create many time the same masked subsystem whith different values of i, in order to be able use the different vector ( varName1, varName2, … ) on Matlab.
Hi Seth,
I have a Simulink/xPC target question. I have a Simulink controller model and would like to bring data in from a CAN link. I would like to put this data into an array, (a circular buffer), and then in my controller I would like to grab elements of the array and perform calculations. Are there Simulink blocks for handling array elements? I know that “Data Store Memory” exists and that they can be arrays but I do not see a way to write in new elements of an array. You can only write to the whole array.
Thanks,
Ron
Hi Seth
I have been using Simulink for about 6 months. I know that you can perform backward integration in Matlab but it does not seem to like it in Simulink, any ideas??? in matlab you simply reverse the time limits and make the time-step negative but simulink does not appear to like this….
any help would be greatly appreciated!!
Thanks
James
I have been sent here by: Doug Hull.
I like your both, ” seth and Dour ” admirabel work. And I need a running, executable m-file for aircraft and helicopter performance and landing controller. Include some explanation
Thank you
ezt
@Jim,
Simulink goes from time =0 to time = Tfinal. If I understand your questions correctly, the easiest way to do this is Simulink would be to simple reverse the data you are integrating. When you import data into Simulink (from say the MATLAB workspace) you provide along with the Data (say 1 column), a time vector ( which should actually be the first column of you data matrix). Now you can simply flip your data (check out the function FLIPUD) and not flip your time vector. Simuink will happily integrate forward in time , but you can always keep at the back of your mind that if the Simulink scope indicates a time of lets say 5.6 sec’s, in your case that would correspond to a time of (Tfinal-5.6) secs ..going backwards.
I am sure there are more elegant ways to do this and I am eager to hear Seth’s take on it, but here is a quick and dirty way to get it done.
Hi Seth,
I am trying to build a matrix with random elements of size a,b using the embedded matlab function. It works if I use y = rand(5,3) in the function, but not y = rand(a,b). What am I missing?
Thanks,
Jeremy
Hi Seth,
Are there any differences in memory usage if you just used the “sim” command without output arguments and used the default save to workspace variables of tout and yout? If you don’t have xout checked in “Configuration Parameters/Data Import/Export” to enable its output we shouldn’t see a performance hit, correct?
Is this alternate method not a preferred method of doing things?
Thanks,
Allan
I realy admire working with simulink for various mechanical simulations
but the published books are very rare
and the no of simulink users is very small compared to those using matlab m files
thnk you
A dedicated blog for Simulink is a great idea!
I work with conversion of legacy C code to Simulink model for control algorithms. I do not have a clue how to implement the pointers in C program into mdl. Is there an easy way?
@Jeremy,
The error you would have got should point you in the right direction. The issue is simple this:
Embedded MATLAB block generates C-code for the block before executing. The fundamental limitation being that dynamic sizing (allowed in MATLAB but not in C ) is not supported.
Therefore, rand(5,4) works because at the time of compilation because the size is defined. rand(a,b) will not work because a and b are only known at runtime. You might have to fall back on the old C trick of declaring a huge random matrix and “selecting” the required dynamic size from that matrix ( there are plenty of Simulink blocks available for this selection operation).
That being said , if you declaring a and b explicitly inside the EML fcn (i.e the values of a and b are not altered by inputs to the block), there should be no issues.
i.e this should work just fine:
function y = fcn()
% This block supports the Embedded MATLAB subset.
% See the help menu for details.
a=2;
b=4;
y = rand(a,b);
Hi Seth,
Congratulations on the new blog. I have been using Simulink for a few years, but I am sure I will learn a lot from this blog.
Future topics that you should consider posting:
1) Incorporating external code within Simulink
2) Creating your own libraries and incorporating them in the Simulink library browser.
BTW – is it a coincidence that you chose to write about a function that rhymes with your name?
:)
Hi Seth, how are you?
I have a doubt about simulink, I don’t know if you can help me, but I’ll say what I need to do…
I want to use the HH:MM block of the Numeric Displays from Gauges library. But when I put this block with some input in it, an error occurs saying that the input have to be an string one. I have no idea on how to work with strings within the simulink. I looked for it in the help, in the internet, in the demos, but I didn’t find how to do it. How can I convert a number to a string in simulink?
I’m modeling a Trip Computer of a vehicle and in somewhere in the model, I have to show the time of the trip based in some clock. I have to show this data in the HH:MM block or similar one.
I would apreciate any help.
Thank you in advance.
Best regards,
Paulo
@Yael - Thank you for suggesting ideas for future posts. Incorporating external code is an important topic many Simulink users need. SET_PARAM… I think you are on to me!
@Paulo - I am not familiar with the Gauges Blockset. I’ll have to ask a colleague about this.
I’m new to Simulink (about 2 weeks into it) and I’ve gotten an assignment that requires me to write a program that will read in a list of signal names and will modify an existing simulink model (using a bus selector going to a mux that outputs a logged signal) to the appropriate values using code. The reason why it needs to be coded is because there are about 7,000 signals coming in and we need to be able to check any given signal to make sure it’s behaving as it should.
I use find_system, get_param, and set_param functions to make the necessary changes. The trouble I’m having is in connecting the bus selector and the mux. I’ve gone in and changed all the port destinations and sources in the ‘PortConnectivity’ block parameter to reflect where the actual lines should be going/coming from but haven’t gotten any results with it. No lines appear in the Simulink model to reflect the changes that are shown in the parameters of the blocks.
Is there a way to create lines using code to connect these two blocks? Is there a better way to take in a huge number of inputs and output a variable number of desired signals to be logged?
Hi Seth.
Thank you for replying.
I already learned that by myself. It’s so easy, but the problem is that the MATLAB documentation does not explain clearly how to do that.
Thank you very much.
hello..
i want to ask how to design serial to parallel block and parallel to serial block in simulink communication blockset for mimo-cdma system?
and also how to plot the bit error rate for mimo-cdma system?tq..
HI!
i am doing work on SIMULINK, let me know if i draw a system model in SIMULINK, it is possible to get the hidden code generated by SIMULINK , because i want to get this code once and want to regenerate a C code form it using REAL TIME WORK SHOP for my final implemetation…..
If you have done some work regarding this …then let me know how it is possible?
@usman,
Real Time Workshop integrates seamlessly with Simulink to produce C code from Simulink models. You really dont have to jump through any hoops (like you describe above)to do this. As long as you have Real Time Workshop installed, you should simply be able to follow the steps listed below to generate code:
1. Open you model in Simulink.
2. Go to Simulation -> Configuration Parameters
3. Under Solver, ensure that you have a fixed step
solver selected.
4. Under Real Time Workshop , click “Build” and watch the
magic happen.
Dear Seth,
Thanks for starting a blog. I barely know how to use Simulink and Matlab, can you point me to a site(s) that could show me some very basic modeling? I want to model some vacuum producing equipment, its just a few simple diff equations, and I need a jump start.
Good job!
@tom - I recommend Vinod’s Getting Started with Simulink Demo Video. This will give you a good overview of the basics of Simulink. There are other web demos to look at on the Simulink demos page. Good luck! Welcome to the blog!
i am using matlab and its image processing tool box since Nov 2005. I want to start work on simulink. This blog is great thing for learners and reseachers. Keep it up.
I can’t understand this tool perfectly.
Hey Seth
I want to implement a limiter for FM demodulation in simulink.dun know how to do it.It is basically limiting from 0 to 1 and a band pass limiter.
Holle sir/miss
i come from Taiwan.
I have a question. I am planning to make the experiment. While needing to join simulink and XPC. A mistake has appeared, it seems to be when real-time workshop, have not supported matlat function ,Can it solved that full of ideas?
http://img244.imageshack.us/img244/3962/l0437f6xd7.jpg
I want to ask, how to utilize simulink to set up charts, and the parameter inside the chart can be kept changing with time?
Thank you!!
hey Seth,
how can i calculate the average of a continous periodic signal , like an output voltage waveform, is there any way i can calculate moving averages as in average for a certain interval each time
Hi Seth,
I am using the While loop(with memory block) to compute the sum of sinusoids, and the results is an input to a state space system. When i run the while loop alone, it runs fast, same as the state space block, but when i combine them i get a terribly slow run. Any tips to make the system faster? Is there any fast alternative to use instead of the while loop?
Hi Seth,
I have landed up in a strange problem. “Parfor” statement for parallel computing toolbox doesnot work inside simulink. I have tried to modify one of my m file s funtion block and it threw this error on my face
Error evaluating registered method ‘Outputs’ of M-S-Function ‘test1′ in ‘test/Level-2 M-file S-Function’. Error using ==> parallel_function>make_general_channel/channel_general at 858
Undefined function handle. The following is the MATLAB call stack (file names and line numbers) that produced this error:
[’C:\Program Files\MATLAB1\R2008a\toolbox\matlab\lang\parallel_function.m’] [752]
[’C:\Program Files\MATLAB1\R2008a\toolbox\matlab\lang\parallel_function.m’] [564]
[’C:\Program Files\MATLAB1\R2008a\work\test1.m’] [354].
I am looking for the interaction between Matlab workspace and Simulink during simulation and after simulation.
Can you please help in understanding the interaction between the two.
Thanks,
-Kusum
hello i want use serial block in simulink of matlab it dosent work and this error is detected how can solve this problem.
please help me
error is:
Error evaluating registered method ‘Start’ of M-S-Function ’sserialsb’ in ‘ode/Subsystem/Serial Send’. Error using ==> sserialsb>Start at 100
The block ‘Serial Send’ cannot be assigned a continuous sample time.
I have a question regarding ‘add_block’ command.
In the help document, it is mentioned that for gain block, the source block’s path is ‘built-in/Gain’ - which works fine.
Could you please let me know the path for the ‘Bitwise Logical Operator’ block from the Simulink library?