which julia version and platform?

Julia 1.2.0 Windows10

Without explicitly calling MSession, can you just do

mat"ver"

to see if Julia will connect to the Matlab engine?

Without explicitly calling MSession, can you just do

mat"ver"

to see if Julia will connect to the Matlab engine?

It reports the error:
MEngineError("failed to open MATLAB engine session")

very odd.

I had to do the following (which is manually/hardcoded for R2020b)

1. clone my version https://github.com/jacob-roth/MATLAB.jl.git
2. add push!(LOAD_PATH,"C:\\Users\\roth0674\\git\\MATLAB.jl") to AppData/Local/Programs/Julia-1.x.x/etc/julia/startup.jl and open REPL
3. from REPL, set ENV["MATLAB_ROOT"] = "C:\Program Files\MATLAB\R2020b\" (you will have to move it to this location if you dont want to edit my fork)
4. ] add "C:\path\to\cloned\MATLAB.jl"
5. ] build MATLAB
6. using MATLAB

Hi, the above mentioned workaround does not work for me. I still get the same error message. Is there another workaround so I can run MATLAB 2020b from julia while in parallel MATLAB2022b installed on my machine?

Hi @VoSiLk !
What operating system and julia version are you using?

What you could try (if not already done):

1. Remove the MATLAB julia package
2. delete existing compiled for MATLAB in the .julia/compiled/<version>/MATLAB directory (the .julia dir should be in %HOMEPATH%\.julia\ or ~/.julia)
3. set the environment variable MATLAB_ROOT (or MATLAB_HOME) to the version you want to use. To check, the resolved path will be $MATLAB_ROOT/bin/<os-arch>/matlab[.exe] so check if this is the correct path (<os-arch> dependes on your system, e.g. win64)
4. install MATLAB.jl again
5. Check that the correct path was used. E.g. try the following julia code: using MATLAB; println(MATLAB.matlab_libpath)
   For me this prints "/Applications/MATLAB_R2023b.app/bin/maca64" (on macos)
6. If the version is correct, check if MATLAB.jl works

One more thing: If you're on Windows, there seems to be an extra step.
The correct MATLAB "server" version must be registered with windows. This should happen automatically at install but if multiple versions are installed this might be the issue

1. Open a new MATLAB window as administrator (with the version you want to use)
2. In MATLAB run !matlab -regserver
3. Close the MATLAB window

The version of MATLAB you opened, should now be the "default" version according to Windows.
So ensure, that this version and the one that MATLAB.jl uses, are the same.

Link to MATLAB docs:

• https://de.mathworks.com/help/matlab/matlab_external/registering-matlab-software-as-a-com-server.html
• https://de.mathworks.com/help/matlab/apiref/engopen.html

Thanks for your help.

The extra step:

1. Open a new MATLAB window as administrator (with the version you want to use)
2. In MATLAB run !matlab -regserver
3. Close the MATLAB window

before

1. Remove the MATLAB julia package
2. Delete existing compiled for MATLAB in the .julia/compiled//MATLAB directory (the .julia dir should be in %HOMEPATH%.julia\ or ~/.julia)
3. set the environment variable MATLAB_ROOT (or MATLAB_HOME) to the version you want to use. To check, the resolved path will be $MATLAB_ROOT/bin//matlab[.exe] so check if this is the correct path ( dependes on your system, e.g. win64)
4. install MATLAB.jl again
5. Check that the correct path was used. E.g. try the following julia code: using MATLAB; println(MATLAB.matlab_libpath)
   For me this prints "/Applications/MATLAB_R2023b.app/bin/maca64" (on macos)
6. If the version is correct, check if MATLAB.jl works

has done the trick :)

My OS is Win11.

Perfect! Thanks for trying (don't have a windows machine to test this) :)

I will push an update the error/help message