I am trying to write an S-Function in Simulink, with the inputs "t" for time, and "LIBs" for the amount of material entering the system. There are 2 outputs. The idea is like this in Simulink.
Simulink model concept
What I want to do is that, at a certain time iteration, the input "LIBs" goes to a different output. But during the iteration, there are some special points at which I don't want the input to go to any output.
The code is like this:
MATLAB
function [Batts_Spent, Batts_N_Spent] = BattsL6Y(t, LIBs)
for t = 2011:6:2035
if t ~= 2005:10:2035
Batts_Spent = LIBs;
end
end
for t = 2015:10:2035
if t ~= 2005:6:2035
Batts_N_Spent = LIBs;
end
end
for t = 2011:6:2035
if t == 2015:10:2035
Batts_Spent = LIBs;
end
end
end
I am sure that this code is not correct, but I don't know how to write it correctly.
And also, even if I have several input and output ports, the S-Function block in the Simulink project still remains only one input and output port. Should I change it to a MATLAB Function block?
In your case t is an input parameter, which makes it look like the function is called for each value of t. Then you have a loop iterating over all values of t. Considering your image, you don't need a loop at all. You can use if in combination with mod. For example:
function [Batts_Spent, Batts_N_Spent] = BattsL6Y(t, LIBs)
if mod(t-2005,6)==0 && t>=2005
Batts_Spent = LIBs;
end
end
This is only "Every 6th time the value of LIBs will be assigned to the first output". This isn't a finished solution but should be sufficient to get you started. You need a second if like this for the other output.
Related
I'm a super beginner in Simulink models and control systems.
I have .slx Simulink model for drone dynamics system.
It takes in two inputs (roll cmd, pitch cmd) and outputs velocity x, velocity y, position x, and position y.
From here, it seems like I can open the system by calling
open_system('myModel.slx', 'loadable');
But how do I put inputs and get output values?
Is there a way I can do this in a gui?
EDIT:
Here is the full layout of my model:
When I did
roll_CMD=10;
pitch_CMD=20;
I got a warning saying:
Input port 1 of 'SimpleDroneDynamics/...' is not connected.
How do I feed inputs using port numbers?
How do I get outputs with port numbers? I tried
[vx, vy, px, py] = sim('SimpleDroneDynamics.slx');
and got an error saying
Number of left-hand side argument doesn't match block diagram...
Is there a way to continuously feed inputs at every time step? This being controller module, I think I'm supposed to feed in different values based on output position and velocity.
EDIT2:
I'm using Matlab2017a
About the first two points of your question:
In simulink:
For the inputs you can use a constant block and when you double click the input block you can assign a value, which can be a workspace variable.
To get the outputs to your workspace you can use the simout block (make sure to put Save format to array).
Connect inputs to your simulink model
Connect outputs of your simulink model to the simout blocks.
MATLAB script
clc;
clear all;
roll = 10;
pitch = 20;
sim('/path_to_simulinkmodel.slx')
time = simout(:,1);
velocity_X = simout(:,2);
velocity_Y = simout(:,3);
position_X = simout(:,4);
position_Y = simout(:,5);
About the third point of your question
You can define the duration of your simulation in the block diagram editor. You can put a variable which is defined in the calling script. There are multiple ways of achieving time dependent input variables:
One option I personally don't recommend is using a for-loop and calling the simulink model with a different value of roll and pitch
for i = 1:numberOfTimesteps
roll = ...
...
sim('simulinkModel.slx')
end
A second and more efficient approach is changing the constant blocks to other source blocks like ramp signals or sinusoid signals
First of all Simulink model use main Matlab workspace. So you can change your variables values at command window (or just at your script) and run Simulink model.
There are several ways to initialize this constants for Simulink. One more useful way is to create script containing all your variables and load it at Simulink model starts. You can do it by adding script name in Simulink/Model Explorer/Callbacks. (There are different callbacks - on Loading, on Starting and etc.). Read more about this: here.
Now you can run your simulation using sim function:
sim('name_of_model')
name_of_model must contain path if model is not in the active MATLAB folder (active folder you can see in your matlab window just under the main menu).
There are different properties of sim function, read about them in help this can be useful for you. By the way: you can change some parameters of your model using sim. You even can find any block in your model and change it's properties. Read more about sim and about finding current blocks. Interesting that the last solution give you ability to change parameters during the simulation!
About getting output. After you run simulation you get tout variable in main workspace. It is an array of timesteps. But if you add outport block (like at my image) you also get another variable in workspace yout. yout is an Datasets. It contain all your outports values. For 2 outports for example:
yout
yout =
Simulink.SimulationData.Dataset
Package: Simulink.SimulationData
Characteristics:
Name: 'yout'
Total Elements: 2
Elements:
1 : ''
2 : ''
Get the values of any of outports:
yout.get(1).Values
it is a timeseries data type, so:
yout.get(1).Values.Time - give you times
yout.get(2).Values.Data - give you values of this outport at each time
We have one more method to take output values:
[t,x,y] = sim('model_name')
it returns double arrays. t- time array, y - matrix of all outports values (it already double and contain only values without times, but for each simulation time!)
So now you can create common Matlab GUI and work at this variables! There is no any difficulties. You can read more about GUI for Simulink here.
I have a Matlab function block in Simulink that receives 2 inputs and processes it to generate an output. During the course of the simulation, at some time points, one of the inputs is zero. I'd like to use the most recent non-zero input to the function whenever that particular input value is zero. How can I achieve this? I tried creating a persisent variable that updates to most recent non-zero input value but that doesn't seem to work.
EDIT 1 (to include code):
function y = fcn(u)
persistent ref_val
if isEmpty(ref_val)
ref_val=10.0
end
if(u(1)<=25)
y=20.0
else
if(u(2)>0)
y=u(2)
ref_val=u(2)
else
y=ref_val
end
end
EDIT 2: For now, I fixed the issue by writing a C code that uses a static variable to retain the most recent non-zero input value. But I still welcome suggestions/solutions to realize this directly in a Matlab function.
Can't you use something like this in your simulation?
//Find the index of the last non-zero value in the input
[~,last_non_zero] = max(find(input(1:i) > 0))
//Call the function using this input
output = fnc(input(last_non_zero))
When I have to display the variable value every n iterations of a for loop I always do something along these lines:
for ii=1:1000
if mod(ii,100)==0
display(num2str(ii))
end
end
I was wondering if there is a way to move the if condition outside the loop in order to speed up the code. Or also if there is something different I could do.
You can use nested loops:
N = 1000;
n = 100;
for ii = n:n:N
for k = ii-n+1:ii-1
thingsToDo(k);
end
disp(ii)
thingsToDo(ii);
end
where thingsToDo() get the relevant counter (if needed). This a little more messy, but can save a lot of if testing.
Unless the number of tested values is much larger than the number of printed values, I would not blame the if-statement. It may not seem this way at first, but printing is indeed a fairly complex task. A variable needs to be converted and sent to an output stream which is then printing in the terminal. In case you need to speed the code up, then reduce the amount of printed data.
Normally Matlab function takes vector inputs as well. This is the case for disp and display and does only take a single function call. Further, conversion to string is unnecessary before printing. Matlab should send the data to some kind of stream anyway (which may indeed take argument of type char but this is not the same char as Matlab uses), so this is probably just a waste of time. In addition to that num2str do a lot of things to ensure typesafe conversion. You already know that display is typesafe, so all these checks are redundant.
Try this instead,
q = (1:1000)'; % assuming q is some real data in your case
disp(q(mod(q,100)==0)) % this requires a single call to disp
I would like to run a Simulink model in a parfor loop on many cores with different data. However, I could not get the sim results when I use parfor whereas I can obtain them while using only for loop.
It simply get [t,u] from workspace1, consider a transfer function n{1}/d{1} and then calculates the EqFracInt to workspace2.
The problematic part of my code is
...
parfor ieq=1:1
assignin('base','t',t);
assignin('base','u',u);
assignin('base','n',n);
assignin('base','d',d);
assignin('base','T_end',T_end);
[simout] = sim('RespSpecFrac', [0 T_end], simset('ReturnWorkspaceOutputs','on'));
PGRs = simout.get('EqFracInt');
end
I could not get the PGRs values. Could you please explain the error to me and how to solve it?
The cause you can't get PGRs values is that is a temporary variable. Since in a parfor loop each iteration is independent, any variable assigned directly inside the loop without indexing is used only in that specific iteration and destroyed.
In order to get the desired values, you need to transform PGRs in either a sliced variable (by indexing it) or in a reduction variable (by, for example, concatenating it). Try to modify the last line of your loop following one of these examples:
PGRs(ieq, :) = simout.get('EqFracInt'); % sliced variable
or
PGRs = [PGRs; simout.get('EqFracInt')]; % reduction variable
The specific implementation will depend on the shape of the expected outputs EqFracInt, of course. You can see more about types of variables inside a parfor loop in the documentation.
I have an ODE for calculating how acidicity changes. Everything is working just fine, only I would like to change a constant whenever acidicity reaches a critical point. It is supposed to be some kind of irreversible effect I wish to simulate.
My constants are coming from a structure file (c) I load once in the ODE function.
[Time,Results] = ode15s(#(x, c) f1(x, c),[0 c.length],x0,options);
The main problem I have here is not telling Matlab to change the constant but remember if it happened already during the simulation once. so Matlab should take the irreversibly changed constant rather than the one I supply at the beginning.
I would like to write a flag that is saved while the ODE is running and an if condition, "if flag exists, change constant". How to do that?
UPDATE I:
PROBLEM SOLVED
Here a first own solution, it is not polished and requires a structure file approach. Which means, the constants which should suddenly changed upon an event, must be struct files which are handed in the ODE function into the function that should be evaluated (look above for the ODE syntax). The function accepts the inputs like this:
function [OUTPUT] = f1(t, x, c)
% So here, the constants all start with c. followed by the variable name. (because they are structs instead of globals)
%% write a flag when that event happens
if c.someODEevent <= 999 && exist ('flag.txt') == 0
dlmwrite ('flag.txt',1);
end
%% next iteration will either write the flag again or not. more importantly, if it exists, the constant will change because of this.
if exist ('flag.txt') == 2
c.changingconstant = c.changingconstant/2;
end
end
Please look into Horchlers kind answer where you have to take care that such a step may introduce inaccuracies and you have to be careful to check if your code does what it is supposed to do.
To do this accurately, you should use event detection within the ODE solver. I can't give you a specific answer because you've only provided the ode15s call it in your question, but you'll need to write an events function and then specify it via odeset. Something like this:
function acidity_main
% load c data
...
x0 = ...
options = odeset('Events',#events); % add any other options too
% integrate until critical value and stop
[Time1,Results1] = ode15s(#(x,c)f1(x,c),[0 c.length],x0,options);
x0 = Results(end,:); % set new initial conditions
% pass new parameters -it's not clear how you're passing parameters
% if desired, change options to turn off events for faster integration
[Time2,Results2] = ode15s(#(x,c)f1(x,c),[0 c.length],x0,options);
% append outputs, last of 1 is same as first of 2
Time = [Time1;Time2(2:end)];
Results = [Results1;Results2(2:end,:)];
...
function y=f1(x,c)
% your integration function
...
function [value,isterminal,direction] = events(x,c)
value = ... % crossing condition, evaluates to zero at event condition
isterminal = 1; % stop integration when event detected
direction = ... % see documentation
You'll want to use the events to integrate right to the point where the "acidicity reaches a critical point" and stop the integration. Then call ode15s again with the new value and continue the integration. This may seem crude, but it how this sort of thing can be done accurately.
You can see an example of basic event detection here. Type ballode in your command window to see the code for this. You can see a slightly more complex version of this demo in my answer here. Here's an example of using events to accurately change an ODE at specified times (rather than your case of specified state values).
Note: I find it strange that you're passing what you call "constants", c, as the second argument to ode15s. This function has strict input argument requirements: the first is the independent variable (often time), and the second is the array of state variables (same as your initial condition vector). Also if f1 only takes two arguments, #(x,c)f1(x,c) is superfluous – it's sufficient to pass in #f1.