I have two Matlab function blocks that one is producing zero signal for the other. I want to store the exact time that signal changes to one in another parameter in order to use it elsewhere.
How can I do it?
This type of functinality is achieved using a Triggered Subsystem, as per the image below,
The output of the trigger block will take on value of the input (which in this case is the simulation time) every time the trigger signal rises. Look at the parameters of the Trigger block inside the subsystem for other options such as falling edge, or both edge, triggering.
Related
Assume that you have a Simulink simulation where a certain signal is first positive and after some time t in a given interval, it becomes negative. Your goal is to find the zero-crossing.
A first approach would be to plot the signal over the given interval, save it and calculate the zero-crossing.
When repeating this simulation numerous times for varying parameters, it would be beneficial to be able to stop the simulation after the signal has become negative. Then there is already enough information for the calculation of the zero-crossing in Matlab. How could you do that?
Yes, use the Stop Simulation block with the appropriate logical input to the block:
You can use an if / else block to control the flow in the Simulink model. In the if / else block, you can choose the condition if u > 0, continue as normal if it's true, and use the else-option to bypass the rest of the flow you would otherwise run. For instance jump directly to the scope.
Another ways:
You can use Hit Crossing Block in Simulink to find time at the moment of hitting zero.
Another way - use any Trigger or Resettable system. It detects the zero crossing too. For example: this question at SO.
Of course you can also use User Defined function to detect zero crossing by your hand and do whatever you want with the signal at the same time.
About making a lot of simulations and then stops:
you can use Check Upper Static Bound for automatically stops simulation at the moment when zero will be crossed in nth time. For example:
I set upper bound = 10 for this block and this stops at 10th crossing.
There are a lot of ways to save function values in this points or just array of times but this is an another question :)
I have a matlab function block (which is not relevant) whose input is his previous output (loop). For example, if in a sample period the output is X, his input in the next sample period will be X, and so on.
This image shows a simplification of my simulation. I initialize the input of my function for the first loop.
The problem is that matlab functions recieves an event based signal from de initialization block in the first sample period (zero-duration), which I must convert to a timed based signal (so I can apply the unit delay that avoids an inifite loop, and allows to generate the next input as explained before). So, when I do so, I lose the information contained in the event-based signal (due to the zero-duration values) and the loop does not work.
If there was a way to intialize the loop in the time-based domain (green part of the image) so, in the first sample time, it is not a zero-duration signal, it would avoid the problem.
Is there any way to do so? Or, a different approach for this problem?
Two approaches come to mind
The initial condition can be set in the Unit Delay block, so it's not clear from your simplified example why you need the specific Initialization block.
You could just use a persistent variable inside the MATLAB Function block to maintain the state from one execution of the block to the next (noting that since it is event driven the block may not get called at every time step, only at each event triggger).
I have designed a signal by using the Signal Builder block in Simulink. During the run of my simulation, the signal builder is to restart depending on the satisfaction of a condition. The condition can be satisfied many times, so, the signal should start from the beginning each time. If I want to put it in another way: You can take step input instead of the designed signal. Step input is to be reset conditionally. How can I make it?
I haven't seen such a functionality built-in Simulink (maybe the newer versions have it?) but here is a workaround:
You can simulate passed time with an integrator that has a Constant block set to 1 as input. The point is that the integrator block has a reset port which you can connect to your condition. So, when your condition becomes true, the integrator restarts a time variable from 0 (which is set in the initial conditions). Beforehand, you need to have your signal saved in something like a Table Lookup block, which outputs the signal as a function of time. Then you connect the integrator output to the Table Lookup block.
Have you tried putting your Signal Builder block in an enabled subsystem? You probably need to set the states when enabling to reset for it to work. Have a look at Create an Enabled Subsystem in the documentation for more details.
I am trying to control a simulink from a M-file.
What I want to do in the M-file is give the simulink model some input, run the simulink model, change one input value at 0.6 seconds, continue running the simulink model with the new input.
I already know that by using set_param, I can start, pause and continue the simulink, but the problem is I don't know how to pause the simulink model at a certain time(0.6s), is it possible to get the current time from simulink model and read it in the M-file?
Another way I already know is using sim to run simulink model from 0 to 0.6s, and use SimState to save the information at 0.6s, then load these information to resume the simulation. I am trying to change the input before the simulation resumed, but it seems that the model will load the input values from the information it saved, it won't take the new input value.
I stuck in this problem for a very long time, could someone help me with this please?
Thank you very much.
You can get the current time of a running simulation with:
get_param('simulink_model_name', 'SimulationTime');
So for instance by checking this value from your M-file during simulation by using
timer(...)
you can detect when the simulation is at 0.6 seconds.
I used a combination of simulink and m-script to achieve a similar goal.
In your model, add one 'assert' block. Double click it, and uncheck 'Stop Simulation when assertion fails'. In the 'Simulation Callback when assertion fails' field, add three commands:
set_param(bdroot,'SimulationCommand','pause');
run('myscript.m'); %insert the script name
set_param(bdroot,'SimulationCommand','continue');
Now connect the inport of this block to a 'not equal to' relational operator. Connect the first inport of the relational operator to a clock (pls set the decimation for analog clock or the sample time [usually -1 for inherited] for the digital clock).
The second inport is connected to constant block with a value of 0.6
On simulating the model, the simulation will pause at 0.6 sec, execute the m-file to change the input parameter (considering that it's tunable) and then continue with the simulation.
The assertion block is called when its input signal becomes 0. At 0.6 sec, the output of the relational operator will be 0.
Let me know if it worked.
This is not currently possible from an M-file. If you want to dynamically change the input at a given time externally, it will require an S-Function. Even this solution is difficult and wrought with flakey-ness since the Mathworks does not want to support this functionality in that it defeats one of the features of another toolbox they sell. In time, I believe they will grant this privledge, but it does not exist today. Also, why not use a dynamic input block to change the input value, like a map, signal builder, etc. ?
I have some questions regarding the simulink model, below.
Given an input in In1, what is the initial input of the 1 tagged in red?
What is the meaning of the block 1/s tagged with 2 in red?
It may be easier to answer these questions in reverse:
2) What is the meaning of the block 1/s tagged with 2 in red?
Answer: This is the Integrator block. It outputs the integral of its input at the current time step. Note that at the first time step, it will output whatever you have specified as its initial condition. By default, I believe that the initial condition is 0. (See the linked doc above for more info on setting various parameters for this block, including initial condition).
1) Given an input in In1, what is the initial input of the 1 tagged in red?
Answer: The initial input at 1 is actually completely independent of In1. It will depend only on the initial conditions of the blocks that feed into it at a given timestep.
You have to take into consideration the execution order of the blocks. In this model, the first block to execute will probably be the integrator block that you have marked with a 2. Following this will be the next integrator block and the gain blocks that they feed. One of the last blocks to execute will actually be the Subtract block that In1 feeds into. This is because this Subtract block needs to know what its input are before it can do any sort of calculations on them, therefore, the other blocks need to execute first.
This may be a little bit confusing considering that there is a loop here and therefore the Subtract block ends up feeding in to the Integrator blocks. This ends up not being an issue because the Integrator blocks do not have direct-feedthrough. This means that the current output of the integrator is not a direct function of the current input. Rather it is calculate based on the current state of the integrator block (which is determined mainly by the input at previous timesteps). This means that the Integrator block doesn't need to know its current input in order to calculate its current output.
So at the first time-step, the output of the integrator block is just the initial condition that you set (or the default initial condition of 0). So most likely, the initial value at 1 is 0.
(This link has some more info on algebraic loops and direct-feedthrough).
See here for more info on execution order in Simulink. This link also shows how to display the execution order in a model, which can sometimes be extremely useful to know.