matlab.eng​ine.Engine​Error: Unable to connect to MATLAB session 'MATLAB_441'.

The situation I have is similar to this. Essentially, I followed this model to have a single container with matlab and python. My code uses start_matlab():

```

class MatlabEngine():

def __init__(self, paths=[]):

self.paths = paths

self.eng = self.startup()

def startup(self):

self.eng = matlab.engine.start_matlab()

for p in self.paths:

self.eng.addpath(p, nargout=0)

return self.eng

```

giving this error: matlab.engine.EngineError: Unable to launch Simple server: Unable to launch /opt/matlab/R2023a/bin/matlab

So I opened a docker and ran `matlab.engine.shareEngine`, and then in a separate terminal, I connected to the same container and was able to run connect_matlab in python directly.

```

>>> import matlab.engine

>>> eng = matlab.engine.connect_matlab()

>>> eng.sqrt(4.0)

2.0

```

However, when I applied the same to my code I get:

```

Traceback (most recent call last):

File "/home/matlab/t-prime/TPrime_transformer/TPrime_transformer_train.py", line 241, in <module>

ds_test = TPrimeDataset_Transformer(protocols=protocols, ds_type='test', file_postfix=args.postfix, ds_path=exp_config["raw_path"], snr_dbs=args.snr_db, seq_len=exp_config["Sequence length"], slice_len=exp_config["Slice length"], slice_overlap_ratio=0, raw_data_ratio=args.dataset_ratio,

File "/home/matlab/t-prime/TPrime_transformer/../preprocessing/TPrime_dataset.py", line 396, in __init__

super().__init__(**kwargs)

File "/home/matlab/t-prime/TPrime_transformer/../preprocessing/TPrime_dataset.py", line 122, in __init__

self.mateng = matutils.MatlabEngine() # todo check if we need any custom paths

File "/home/matlab/t-prime/TPrime_transformer/../preprocessing/matutils/matutils.py", line 8, in __init__

self.eng = self.startup()

File "/home/matlab/t-prime/TPrime_transformer/../preprocessing/matutils/matutils.py", line 17, in startup

self.eng = matlab.engine.connect_matlab()

File "/home/matlab/t-prime/TPrime_transformer/../matlab/engine/__init__.py", line 188, in connect_matlab

eng = future.result()

File "/home/matlab/t-prime/TPrime_transformer/../matlab/engine/futureresult.py", line 67, in result

return self.__future.result(timeout)

File "/home/matlab/t-prime/TPrime_transformer/../matlab/engine/matlabfuture.py", line 87, in result

handle = pythonengine.getMATLAB(self._future)

matlab.engine.EngineError: Unable to connect to MATLAB session 'MATLAB_441'.

```

[Infinite_king]

Hi Hud Bin, what type of MATLAB license do you have?

Answer 1

[Infinite_king]

Hi Hud Bin,

Based on your description, it seems you are attempting to connect to the MATLAB engine from Python using 'matlab.engine.start_matlab()', but this approach is encountering errors. The connection works successfully if the MATLAB session is started manually and then converted into a shared session.

Try the following steps and see if it works,

• Close all running sessions of MATLAB.
• Open a new MATLAB session and enter 'matlab.engine.shareEngine' to convert it into a shared session.
• Alternatively, you can use the command "matlab -r "matlab.engine.shareEngine" from the terminal to start MATLAB in shared mode.
• Create a sample Python file to connect to the shared session using 'matlab.engine.connect_matlab()'. For example

# sample.py
import matlab.engine
eng = matlab.engine.connect_matlab()
eng.sqrt(4.0)

• Run the Python file. If it runs successfully, it means the connection to MATLAB has been established.
• Note - Keep the MATLAB session running in the background.

Additionally, if you still want to use 'matlab.engine.start_matlab()', try the following:

1. Close all running sessions of MATLAB.
2. Create a sample Python file to start and connect to the MATLAB session

# sample2.py
import matlab.engine
eng = matlab.engine.start_matlab("-desktop")
eng.sqrt(4.0)

For more information refer the following MATLAB documentations -

Connect Python to Running MATLAB Session - https://www.mathworks.com/help/matlab/matlab_external/connect-python-to-running-matlab-session.html

Starting MATLAB Engine - https://www.mathworks.com/help/matlab/apiref/matlab.engine.start_matlab.html

Hope this is helpful.