How to run Simulation for certain amount of time

Hello,

i want to run my Simulation for a certain amount of time and then pause it. I tried with an assertion block which works fine but if i start the simulation through python the assertion block doesn't stop the simulation. Is there a work around?

kind regards

Answer 1

[Fangjun Jiang]

Specify the start time and stop time either directly through numerical value, or through variables and then set the value for the variables.

[Peter Pallasch]

Well that's also a possibility. But i have to restore the old state after the simulation time. Because i want to execute the simulation in steps. So either i run the simulation for some time and then pause it and continue. The other possibilty is like you said to start the simulation and stop it after some time, safe the state and then restart the simulation at that position. So the other possibilty i also tried.

That's my code for the safe state and restart simulation. The problem here is that simOut is None.

while True:    
    simOut=eng.sim('model','SaveFinalState','on','FinalStateName','myOperPoint','SaveFormat','Structure','SaveOperatingPoint','on','SolverType','Variable-step','StartTime','0.0','StopTime', '0.005', 'MaxStep', '1e-3',nargout=0)
	print(simOut)
	myOperPoint = simOut.myOperPoint
	
	print("execute some code")
	time.sleep(20)
	
	eng.set_param('model','LoadInitialState','on','InitialState','myOperPoint')
	myOperPoint = simOut.myOperPoint
    
    

The other solution with the pause is to use an assertion block but like i said its not pausing if i start it in python. here is my code for the pause solution.

import matlab.engine
import sys
import os
import time
from threading import Thread
import subprocess
import time




eng = matlab.engine.start_matlab()

Thread(target=eng.sim,args=('model', 'SolverType', 'Variable-step','StartTime', '0.0', 'StopTime', 'inf', 'MaxStep', '1e-3')).start()


#While the simulation is running
while eng.get_param('model','SimulationStatus')!=('stopped' or 'terminating'):
    print("inside while",flush=True)
    if eng.get_param('model','SimulationStatus')=='paused':
        print("detected pause",flush=True)
        
        print("Do something")
        eng.set_param('model','SimulationCommand','update',nargout=0) #if you have updated any simulation parameters
        eng.set_param('model','SimulationCommand','continue',nargout=0)

print("end",flush=True)

The pause assertion solution has two problems. The first one is that the assertion block doesn't pause the simulation. The 2nd one is that the code after the line:

Thread(target=eng.sim,args=('model', 'SolverType', 'Variable-step','StartTime', '0.0', 'StopTime', 'inf', 'MaxStep', '1e-3')).start()

is not executed properly.

Thank you for your help

[Fangjun Jiang]

"The problem here is that simOut is None."

I wonder if it is related to this issue which happened a few times already.

https://www.mathworks.com/matlabcentral/answers/721599-problem-with-simscape-variable-visibility

If it is, then you won't be able to use eng.sim(). You probably need to use run a "eval()" line or run a simple M-script file.

[Peter Pallasch]

First thank you for your help!

Actually it was very hard to find something on this topic. I was seaching for days but i found an article. For everyone who has the same problem. You just start/pause the Simulation by setting the parameters directly. No need for the sim command.

Here is my example code:

import time
import matlab.engine


sys.path.append("c:\work\matlab19bPy36")

eng = matlab.engine.start_matlab("-desktop")

eng.run(nargout=0)



eng.eval("model = '{}'".format("modelname"),nargout=0)
eng.eval("load_system(model)",nargout=0)
        

print("Initialized Model")
        
#Start Simulation and then Instantly pause
eng.set_param("modelname",'SimulationCommand','start','SimulationCommand','pause',nargout=0)

while True:
	eng.set_param("modelname",'SimulationCommand','continue',nargout=0)
	print("Continue")
	time.sleep(30)
	eng.set_param("modelname",'SimulationCommand','pause',nargout=0)
	print("stopped")
	time.sleep(30)

Here is a link to the article that helped me. The guy build a little controller to control the simulation via python:

Controlling a Simulink Model by a Python Controller | by Soutrik Bandyopadhyay | Medium

[Urveshkumar Dharmendrabhai]

Thank you for your answer. Would you please clarify what is a

time

in your answer? How and where have you defined 'time' variable?

[Peter Pallasch]

"time" is not a variable. Its a python module if you refere to the line of code:

import time

time.sleep(30)

The whole point of this Setup was to discretize time. Hence you start your matlab simulation via:

eng.set_param("modelname",'SimulationCommand','continue',nargout=0)

use the python time module to wait 30 seconds by using the python time module via:

import time

time.sleep(30)

and then stop the simulation again via:

eng.set_param("modelname",'SimulationCommand','pause',nargout=0)

Then you can make calculations with the collected data and you have descrete time where every timestep is equal to about 30 secs. The whole thing is controlled via python. Matlab has a python library for that purpose which is included as python module via:

import matlab.engine

All code shown here is no matalb code. I also updated the example code which i think you were refering to. I hope this helps!