I am running a simulink simulation using the fixed-step discrete solver. I've even specified the fixed-step size. I save some data via a "To Workspace" block (I've used the Scope to save to workspace as well with equivalent results). When I look at the time data in the object, the time is not monotonically increasing.
The time value is constant for 5-10 samples, then continues. Any ideas why this happens?
I took a screen shot of the Time vector. You can see it goes flat, then continues, then is flat. I expected a single line.
I asked on the Mathworks site as well. I'll update both if I get an answer.
EDIT: I am working with Mathworks now too. They did show me how to visually inspect sample times. Navigate to Format > Sample Time Display > All. This will show all of the sample times in the simulation.
This problem was caused, at least partly by the existence of algebraic loops. Since Simulink was recalculating the algebraic loops, the output was capturing these changes.
I was able to click the "minimize algebraic loop occurrences" in the
Configurate Parameters > Model Referencing
and my loops were eliminated. This is a YMMV answer, but its the best I've found working with Mathworks support.
Related
I know it sounds strange and that's a bad way to write a question,but let me show you this odd behavior.
as you can see this signal, r5, is nice and clean. exactly what I expected from my simulation.
now look at this:
this is EXACTLY the same simulation,the only difference is that the filter is now not connected. I tried for hours to find a reason,but it seems like a bug.
This is my file, you can test it yourself disconnecting the filter.
----edited.
Tried it with simulink 2014 and on friend's 2013,on two different computers...if Someone can test it on 2015 it would be great.
(attaching the filter to any other r,r1-r4 included ''fixes'' the noise (on ALL r1-r8),I tried putting it on other signals but the noise won't go away).
the expected result is exactly the smooth one, this file showed to be quite robust on other simulations (so I guess the math inside the blocks is good) and this case happens only with one of the two''link number'' (one input on the top left) set to 4,even if a small noise appears with one ''link number'' set to 3.
thanks in advance for any help.
It seems to me that the only thing the filter could affect is the time step used in the integration, assuming you are using a dynamic time step (which is the default). So, my guess is that (if this is not a bug) your system is numerically unstable/chaotic. It could also be related to noise, caused by differentiation. Differentiating noise over a smaller time step mostly makes things even worse.
Solvers such as ode23 and ode45 use a dynamic time step. ode23 compares a second and third order integration and selects the third one if the difference between the two is not too big. If the difference is too big, it does another calculation with a smaller timestep. ode45 does the same with a fourth and fifth order calculation, more accurate, but more sensitive. Instabilities can occur if a smaller time step makes things worse, which could occur if you differentiate noise.
To overcome the problem, try using a fixed time step, change your precision/solver, or better: avoid differentiation, use some type of state estimator to obtain derivatives or calculate analytically.
how to import a bitsream form binary vector from workspace into simulink.Actually I have found that I can use simin block or In block but my binary vector is independant of time. I tried to use Const block and it works but afer that when I wanted to put my output in the Buffer block in simulink, it didn't work because the input is continuous and not discrete. So I am asking if it's a way to add time to my binary uni-dimensional without having any influence on the result?and how can I do it?
Or is there another way to import this date to avoid this problem with Buffer block?
Your screenshot shows your constant block to have a sample time of Inf. As the error message suggest, you need to change that to a discrete sample time. In addition, you should also:
check your model is using a fixed-step solver
check what time step you are using for your chosen fixed-step solver (ideally the same as your constant).
You can have multi-rate models, but you need to manage the rate transitions with Rate Transition blocks. For more details on sample times, see the documentation, in particular how to view sample time information in a Simulink model. You should probably also have a quick look at the Choose a Solver section.
I am trying to make a simulation in Simulink, with the fuzzy model.
As inputs, I have set four time series variables from the workspace (compatible to simulink after performing Simulink.Timeseries function): every row of the variables has a linked time starting from 0 to 10566 (seconds, I believe). How can I set the sample time in simulink source block in order to pick every exact case without interpolation?
Thank you for your kind answers,
Phalaen
Are you using the From Workspace block? If so, it's simply a matter of specifying the sample time in the block parameters and unticking "Interpolate data". You can also display the sample time information of the model to check which sample time each block is using, see View Sample Time Information in the documentation.
I have a model and I need to change the sample time of each block that I currently have in my Simulink model.
The problem is that I have so many blocks that make changing this parameter for each individual one cumbersome. Is there a means to change it for a group of blocks?
One more thing, what is the default sample time indicated by "-1"?
This can be done quite easily. In general it is a good practise to be aware of the simulation time, simulation steps and solver you are using in simulink simulations, as sometimes the simulation can go wrong just because of the solver, or because of the simulation step size.
To change all this parameters (and the step size, what I assume is your "sampling time")
you need to go to the Solve Pane that looks like this:
You can see in there how "Max step size" and "min step size" are there, set to auto. This two exist because some odes (as ode45 in this case) use variable step size, but if you want fixed step size you can change the solver to ode1 or ode3 for example.
About that -1 thing... You should not change each blocks sample rate unless you really meant to. When do yo want to do this? In general when you want the sample rate of THAT specific block to be smaller than the rest. So if you have a simulation that is running the whole system at 1e-2 sample rate, and you have an specific block thatneeds to run just every second, then you change the sample rate. Else the default is -1, which means the same sample rate that you have set up in the Solve Pane.
So:
ALWAYS be aware of whats going on in the Solve Pane
Dont change those "-1" unless you really meant to
I am solving a stiff PDE in MATLAB using ode15, and it often freezes depending on the initial conditions. I never actually get an error, it just won't finish even after 10 hours when it should take around 30 seconds to run. I am experimenting with different spatial and time node intervals, but it is hard, because I don't get feedback.
Is there some sort of equivalent to diagnostic for fsolve? stats is not useful because it only displays an output after fsolve is finished.
Check out the documentation on odeset, and specifically the stats option. I think you basically just want to set stats to on and you will get some feedback.
Also, depending on your ODE, you may need a different solver. About half way down the page on this page there is a list of most of the solvers available in MATLAB. Depending on whether your function is stiff or non-stiff, and how accurate you need to get, one of those might work better for you. Sometimes I just code them all in and comment out all but one until I find the one that runs the best for me, but check out the documentation on each if you want to find the "right" one for your application.
Your question is confusing because you refer to both ode15s and fsolve locking up. These are two completely different functions. One does numerical integration and the other solves for roots. Also, fsolve has no option called 'Stats' (see doc fsolve). If you want continuous output from fsolve use:
options = optimist('Display','iter');
[x,fval,exitflag] = fsolve(myfun,x0,options)
This will display the iteration count, number of function evaluations, the function value, and other stuff depending on what algorithm you use (the alorithm can be adjusted via the 'Algorithm' option). Again see doc fsolve for full details.
As far as the 'Stats' option with ode15s goes, it's not going to give you very much information. I doubt that it will you figure out why your system is halting (if it even is ode15s that you have a problem with). What you can try is using an output function via the 'OutputFcn' option of odeset. You can try the simple odeprint first:
options = odeset('OutputFcn',#odeprint)
which will print your state after each integration step. Type edit odeprint to see the code and how you might write your own output function if you need to do more.