I have a MATLAB function block in simulink and for each step simlulink does I want to input a counter with increment 1.
Ex:
1st Step -> Acc=1
2nd Step -> Acc=2
I tried using a Count up block + Pulse generator but the time step of simulink is not constant.
Any ideas?
A common way to do this is to use a sum and a memory block with an initial condition of 0. It should count steps in both fixed and variable step simulations. In fact I believe this would be build and perform very much like an s-function solution during simulation.
Why not just use an integrator block? You can choose with a discreet or continuous integrator block depending on your model type. You can specify the start conditions/value and reset conditions if needed. The image below shows an example of discreet and continuous blocks. Both are just using their default values. To do what you want (adding 1 to the output every step) just define the model sample time as an environment variable (eg sT=0.01) and set the integrator gain to be 1/sT.
Related
Im trying to do some calculations in a Matlab (R2015b) Simulink function block. I use a signal that gives discrete values in 1-minute intervals.
What i want to do is store the signal values of 1 day (1440 values), convert them into a vector and input it in my Matlab function for calculation (getting time between first and last value > x). All while the simulation is running.
Unit delay, and Transport delay blocks wont work because i need all the stored values at once.
Any ideas on this are much appreciated!
Thanks!
You need to add a "To Workspace" block to your simulink diagram. Setting the options as you wish will allow you to save all the outputs in a single vector. You can select the variable's name, and the default is "simout".
Then, after running the diagram, you have the variable you want in the workspace (as if you had typed it in the console). So next, you can call your function with the argument.
I have simple Simulink model and I would like to change the initial condition of integrator based on some signal. This signal can take values 1 or 0 and initial conditions of integrator should be equal to 1.16 or 0.65 respectively.
I tried to set a parameter x_init in Model Workspace (and then use it in Integrator block), but I couldn't access it via function. Then I tried to run MATLAB function inside simulink model with set_param(...), but I got error:
Function 'set_param' is not supported for code generation. Consider adding coder.extrinsic('set_param') at the top of the function to bypass code generation.
This is how the structure of model looks like in Model Explorer. I would like to change the x initial condition.
Using a workspace variable as you are doing is the wrong approach.
Change the Initial Condition Source property of the integrator to external. This will give the block an additional in port. The value of the signal fed into this port when the integrator is reset is taken as the initial condition.
I'm trying to model the respective processes of an internal combustion engine. My current modelling approach is to have different sub functions which model the different processes.
Within each sub function is a Level 2 S-Function which solves the ODEs to give the in cylinder state (pressure, temperature, etc).
The problem that I'm having is that each sub function is enabled depending on the current crank angle which is computed from the current timestep in Simulink. The first process works fine as I manually set the initial values, but then I can't pass the latest in-cylinder state (the output from the first sub function) to the second sub function to use as the initial conditions (it insists on using the initial values I set at the beginning of the simulation).
Is there any way round this? Currently I'm going along a path of global data stores, but haven't had any joy so far.
There are a lot of different ways to solve this problem.
I'll show some of them as examples.
You can create additive output with Unit dalay block like this:
So you can get value of your crank angle from previous timestep and USE IT in formula for solving you equations.
Also you can use some code like this:
if (t == 0)
% equations with your initial values
sred = 0;
else
% equations with other values
y = uOld + myCoeef;
end
Another idea: sometimes I use persistent variables in Matlab function to save values of some variable from previous step. But I think it makes calculation slower.
One more idea - if you have Stateflow you can create chart with two states: first for initial moment with your coefficient and second to solve new equations.
If I understood you in wrong way you can show your code and we'll offer some new ideas!
P.S. Example of my using of S-Function:
My S-Function needs 2 values: Q is calculated in simulink at every step, ro is initial I took from big matrix I loaded from workspace in table and took necessary value depending of time.
So there is no any initial values in S-Function - all needed values I transmit into it from simulink!
In simulink I have a function block. Basically it contains
function y=fcn(u)
if u==1
a=[0,...,1];
b=[1,...,2];
end
y=[a',b'];
%y=struct('time',a,'value',b); %Second option
I want to use these arrays as a signal. As you see I have tried two options, making an output as an array and as a structure, non of them work for me.
In short, I'd like to be able to connect a scope to the output of the function and see the signal generated by (a,b). The reason I want to do it from a Simulink block is that I can just switch between many options of signals without having to build again the model. More over, I'd prefer that if the simulation time is bigger than whatever is specified in a then the signal keeps the last value of b.
p.s. I have tried this using a From Workspace block and it works fine.
Question
Is there a way to enforce the simulation step to be smaller than a compile-time constant in a simulink model?
Context
I'm trying to build a PWM block on simulink. As it is now, I have to make sure that the user chooses a step size responsibly (smaller than half the period chosen by him), otherwise the block behaves abnormally. The only way I came up was to stop the simulation if the step size is not small enough, but I find that very annoying (as a user). If possible, I'd like for the user to not worry about this at all.
Here's what I would do: add the following pseudo-code to the block callback StartFcn:
T_PWM = get_param(gcb,...); % get the block parameter (period) of the current PWM block (string)
T_PWM = str2double(T_PWM);
T_solver = get_param(bdroot,'FixedStep'); % get fixed used by the solver (string)
T_solver = str2double(T_solver); % convert from string to double
if T_solver > 0.5*T_PWM
error('Solver step size must be smaller than half the PWM period')
end