MATLAB: Matlab.engine.start_matlab() takes long time to execute even if MATLAB session already exists

delaylongMATLABmatlab.engine.start_matlab

Following MATLAB instructions on how to integrate MATLAB with python, we’re using the following syntax

*import *matlab.engine
future = matlab.engine.start_matlab(async=*True*)
self.eng = future.result()

However, either in async or in sync modes , even if MATLAB has been already started and we’re trying to connect to an existing session, it takes about 40 sec

for matlab.engine.start_matlab function to execute.

Best Answer

_ matlab.engine.start_matlab() _function starts a MATLAB session. So, if it is taking too long, it is possible that MATLAB itself takes few seconds to start.

matlab.engine.start_matlab() always starts a new MATLAB process, and returns Python variable eng, which is a MatlabEngine object for communicating with the MATLAB process.

You can quickly test the same on a Windows enviroment.

When you call _matlab.engine.start_matlab(), _it will start a new MATLAB process always.

If no argument is passed, it will open a background process.

To confirm that this functions starts a new session always (even though MATLAB session is currently running), please start using "-desktop" option-

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

You will see that a new MATLAB Session has been started.

If no option is used, you can see MATLAB in background process.

Run the following command in MATLAB command prompt

>> which -all startup.m

It will show you if you are using any startup file.

Sometime startup file can cause delay.

If you see any startup.m file, try to rename it and try connecting MATLAB engine from Python.

Related Solutions

MATLAB: Do I receive the error “TypeError: unsupported data type returned from MATLAB” when attempting to load a .mat file in Python

This error message occurs when your .mat file contains variables with types unsupported by the MATLAB API for Python.

When a MATLAB function, called via the MATLAB Engine API for Python, returns output arguments, the API converts the data into equivalent Python data types. However, not all MATLAB data types can be converted. The following MATLAB data types cannot be converted, and thus cause an unsupported type or value error when they are returned:

- Categorical array

- char array (M-by-N)

- Cell array (M-by-N)

- Function handle

- Sparse array

- Structure array

- Table

- MATLAB value objects

- Non-MATLAB objects

One workaround involves using the "evalc" function, via MATLAB Engine, to call the "load" function (instead of calling the "load" function directly). What this allows you to do is keep the loaded variables in the MATLAB Engine workspace so that the API does not attempt to convert them to Python data types. Then you can pull the variables from the MATLAB Engine workspace into the Python environment, as needed, after doing any necessary conversion.

For example:

import matlab.engine
eng = matlab.engine.start_matlab()
# Use evalc to load the .mat file so that it is kept in the MATLAB Engine workspace.
# This stops the API from attempting to convert the variables Python types on load.
eng.evalc("s = load('my_file.mat');")
# Now we can grab the data, as needed, from the MATLAB Engine workspace and pull it into Python.
# At this point the API will need to convert the data to Python types.
myVar1 = eng.eval("s.myVar1");
print (myVar1)
# With unsupported types, we can convert the variables to supported types while they are in
# the MATLAB Engine workspace, and then pull the supported representation into Python.
eng.evalc("dt = num2cell(s.myDatetimes)")
myDateStrings = eng.eval("cellfun(@datestr, dt, 'UniformOutput', false)")
print (myDateStrings)
eng.quit()

MATLAB: Is it possible to suppress the MATLAB Command Window from opening when you launch the MATLAB Engine using MATLAB 7.8 (R2009a)

The ability to suppress the MATLAB Command Window when starting a MATLAB Engine session is not available in MATLAB.

As a workaround, you can hide the command window once it has been opened using the ENGSETVISIBLE function. The following lines of code illustrate how you can do this:

Engine *ep;
ep = engOpen(NULL);
engSetVisible(ep, 0);

Best Answer

Related Solutions

MATLAB: Do I receive the error “TypeError: unsupported data type returned from MATLAB” when attempting to load a .mat file in Python

MATLAB: Is it possible to suppress the MATLAB Command Window from opening when you launch the MATLAB Engine using MATLAB 7.8 (R2009a)

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