Python call matlab function 'plot', The figure disappeared in few seconds.

Question

Tianya Duan 2020-3-24

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/512567-python-call-matlab-function-plot-the-figure-disappeared-in-few-seconds

回答： Nihal 2024-7-24

When I use python call the matlab funtion plot, the figure only exists few seconds, then it colsed automatically. Why does have this phenomenon occur? How could I change or add something? Thank you very much.

AddTset.m

function c = AddTest(a,b)
   c = a + b;
   figure(1)
   plot(a,c,'DisplayName','test');
   %pause(30);
end

pyCallMat.py

import matlab.engine
if __name__ == '__main__':
    eng = matlab.engine.start_matlab()
    a = eng.AddTest(1.0,2.0) 
    print(a)
    b = eng.sqrt(4.) 
    eng.figure(3.0)
    eng.plot(a, b, nargout=0)
    print(b)

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Tianya Duan 2020-3-26

在 MATLAB Online 中打开

The question has been solved by Chinese matlab support team.

Two methods:

add a line of the following command

input("Press Enter to continue...")

2. use the following answer of the website

isvalid function is more useful if you want to write a GUI.

while eng.isvalid(h):
    pass

Villa Xue 2022-3-11

Thank you a lot, It works when use: input("Press Enter to continue...") in python

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Answer 1

Nihal 2024-7-24

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/512567-python-call-matlab-function-plot-the-figure-disappeared-in-few-seconds#answer_1489816

在 MATLAB Online 中打开

The issue you're encountering is likely due to the fact that the MATLAB engine for Python does not keep the MATLAB session open once the Python script finishes executing. As a result, any figures created in MATLAB are closed when the session ends.

To keep the MATLAB figure open, you can use the matlab.engine's blocking parameter to keep the MATLAB session alive. Another approach is to add a pause in your MATLAB function to keep the figure open for a specified amount of time.

Solution 1: Using pause in MATLAB Function

You can add a pause statement in your MATLAB function to keep the figure open for a specified duration:

matlab

function c = AddTest(a, b)
c = a + b;
figure(1)
plot(a, c, 'DisplayName', 'test');
pause(10);  % Pause for 10 seconds
end

Solution 2: Keeping MATLAB Session Alive

Modify your Python script to keep the MATLAB session alive using the blocking parameter:

python

import matlab.engine
if __name__ == '__main__':
    eng = matlab.engine.start_matlab()
    a = eng.AddTest(1.0, 2.0, nargout=1)
    print(a)
    b = eng.sqrt(4.0)
    # Keep the MATLAB session alive
    eng.set_param('0', 'SimulationCommand', 'start', nargout=0)
    input("Press Enter to close MATLAB session...")
    eng.quit()

Solution 3: Using matplotlib for Plotting in Python

If you don't need to plot in MATLAB specifically, you can use Python's matplotlib to plot the results. This way, you keep the plotting within the Python environment:

python

import matlab.engine
import matplotlib.pyplot as plt
if __name__ == '__main__':
    eng = matlab.engine.start_matlab()
    a = eng.AddTest(1.0, 2.0, nargout=1)
    print(a)
    b = eng.sqrt(4.0)
    # Plot using matplotlib
    plt.figure()
    plt.plot([1.0], [a], label='test')
    plt.xlabel('a')
    plt.ylabel('c = a + b')
    plt.title('Plot of a vs c')
    plt.legend()
    plt.grid(True)
    plt.show()
    print(b)

Summary

Solution 1: Add a pause statement in your MATLAB function to keep the figure open for a specified duration.
Solution 2: Modify your Python script to keep the MATLAB session alive using the blocking parameter.
Solution 3: Use Python's matplotlib for plotting instead of MATLAB.

Choose the solution that best fits your needs. If you still want to use MATLAB for plotting, Solution 1 or Solution 2 would be appropriate. If you are open to using Python for plotting, Solution 3 is a good option.