Python can't send value to simulink constant block

This is my simulink. I want to send the value from my python to constant block of u1 and u2, then the x1 and x2 will send the output to my python. Please ignore u2, cuz still in testing phase.

this is part of my python code, the set control action is used to send the value to u1 and u2 in simulink. This is the issue where the simulink cant access to the value sent from python. The output dont have issue.

Here is the output, as shown above the output x1 is showing 1.0 which shows that the constant block is not deliver the input values from python.

SO is there anyway to solve this issue? anything i need to check or set in the simulink? or any website or code I can refer to? any help or recommendation will be appreaciate. Thank you very much.

Answer 1

[Ayush Singh]

Hi Yeow,

I am assuming you want to assign values to constant blocks u1 and u2 from Python and extract values of x1 and x2 after some simulation on your model.

In order to achieve the workflow mentioned by you there are roughly 3 steps can follow:

1. Set values to the constant blocks u1 and u2 from Python.
2. Run the Simulink model.
3. Retrieve the outputs x1 and x2 from the MATLAB workspace back to Python.

Start the MATLAB engine

eng = matlab.engine.start_matlab()

Load the Simulink model

eng.load_system(model_name, nargout=0)

Set values to the constant blocks u1 and u2

eng.set_param(f'{model_name}/u1', 'Value', str(u1), nargout=0)
eng.set_param(f'{model_name}/u2', 'Value', str(u2), nargout=0)

Run the Simulink model

eng.set_param(model_name,SimulationCommand="start")

Wait for the simulation to finish

eng.set_param(model_name,SimulationCommand="stop")

Retrieve the outputs x1 and x2

x1 = eng.eval('out.x1', nargout=1)
x1_data =x1.Data
x2 = eng.eval('out.x2', nargout=1)
x2_data =x2.Data

The above steps/code might not be exactly according to your coding structure but is a rough idea/implementation on how you can achieve the desired workflow.

I hope it helps you to get started!

Answer 2

[Yeow Yu Leong]

Hi @Ayush Singh, Thanks for your reply.

Currently, I am using another structure to extract and send the data. Is working for me. Here is my code:

import matlab.engine

import numpy as np

import time

###this one is working 5/7/24

# Start MATLAB engine

eng = matlab.engine.start_matlab()

# Load the Simulink model

eng.load_system('tracking3')

# Main loop to send random input and retrieve output

num_cycles = 500 # Number of simulation cycles

for cycle in range(num_cycles):

# Generate a random value for the constant block

u1_value = np.random.random()

# Set the value for the constant block 'Constant'

constant_block_path = 'tracking3/Constant'

eng.set_param(constant_block_path, 'Value', str(u1_value), nargout=0)

# Run the Simulink model

eng.set_param('tracking3', 'SimulationCommand', 'start', nargout=0)

status = eng.get_param('tracking3', 'SimulationStatus')

while status != 'stopped':

status = eng.get_param('tracking3', 'SimulationStatus')

# Retrieve the output value from 'x1' in 'out'

x1_value = eng.eval('out.x1')

first_x1_value = x1_value[cycle][0]

print(f'Cycle {cycle+1}: Input = {u1_value:.4f}, Output = {first_x1_value:.4f}')

# Pause for a moment before next cycle (optional)

time.sleep(0.1) # Adjust as needed

# Close the Simulink model without saving

eng.close_system('tracking3', 0, nargout=0)

# Stop MATLAB engine

eng.quit()