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).
Related
In the model, I need to time segments in which some agents go through, but not all, rendering the use of timeMeasureStart and End blocks ineffective as any agents who go through a certain End block MUST go through it's corresponding Start block, but not all agents that will encounter the End block will have gone through it's corresponding Start block.
I have done the following and receive the error that 'agent cannot be resolved to a variable' in the Histogram
Defined the variables startTime endTime cycleTime in the agent class Patient which is being pushed through the model.
Put agent.cycleTime=agent.endTime-agent.startTime; in the On enter slot of the block in which I want the timing to end.
Defined a Histogram Data called myDataSet with the Value agent.cycleTime in Main
Made a histogram in Main which takes myDataSet in it's Histogram slot.
First, you can still use TimeMeasureStart/end blocks. Just let some agents bypass them with a SelectOutput block upstream of the TimeMeasureStart block. The condition would be determined by who should be measured.
Ok, then to your details:
Put agent.cycleTime=agent.endTime-agent.startTime; in the On enter slot of the block in which I want the timing to end.
This is not how you would measure time. The variables are a good start, though. Do this instead:
Wherever timing should start, you write agent.startTime = time() (logs curr model time)
Wherever timing should end, you write agent.cycleTime = time() - agent.startTime, essentially measuring how much time has passed since the start.
Now you do what you want with agent.cycletime
Defined a Histogram Data called myDataSet with the Value agent.cycleTime in Main
this is not how you use Histogram Data. You need to use the API calls on it properly, for example myHistogramData.add(someValue):
Also, always check example models and the help, many issues can be solved by checking those first :)
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.
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 system with some embedded Matlab blocks where I'd like to perform some actions after a certain amount of time, in this case turn on lights and switches in an interface to which I send signals from Simulink.
The problem is that I thought I'd use "tic"-"toc" and "while" in a Matlab function block to perform these actions, say one parameter becoming 1 after 5 seconds, the following parameter becoming 1 after 12 seconds and so on, but I noticed that tic-toc apparently doesn't work in Simulink for embedded functions.
Is there any similar functions that could be used in Simulink for embedded functions or is there any other way to do this?
Edit: I've tried to get the clock's time as well, but it's a growing value. Is there any way to "lock" the time as a parameter when the block's function is executed?
You shouldn't be using absolute time in an embedded system, which is at least one of the reasons why tic-toc and clock from MATLAB don't work with Simulink Coder.
You should create your own counter, which you start and stop when you need to.
This is pretty easy to do using a Unit Delay and Summation block.
If you need to be able to enable and/or reset the counter then use the appropriate block from the Additional Discrete library.
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.