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problem with python numpy

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Johann Thurn
Johann Thurn on 31 Oct 2018
Commented: Binxu on 8 Oct 2020
I have started to try to use python functionality in matlab. The Textwrapper example works. I now tried other packages, and everytime there is some dependency on numpy I get this message:
>> py.help('numpy')
problem in numpy - ImportError:
Importing the multiarray numpy extension module failed. Most
likely you are trying to import a failed build of numpy.
If you're working with a numpy git repo, try `git clean -xdf` (removes all
files not under version control). Otherwise reinstall numpy.
Original error was: DLL load failed: Das angegebene Modul wurde nicht gefunden.
If I try to use numpy directly, I get this:
>> x = py.numpy.random.random([4,4]);
Undefined variable "py" or class "py.numpy.random.random".
Calling
help('textwrap')
or
help('numpy')
in Python works fine. Calling
py.help('textwrap')
in Matlab works,
py.help('numpy')
does not.
I have tried to update numpy and to remove and reinstall it, but this does nothing. I am using Python 3.6 which should be supported.
>> pyversion
version: '3.6'
executable: 'C:\ProgramData\Anaconda3\python.exe'
library: 'C:\ProgramData\Anaconda3\python36.dll'
home: 'C:\ProgramData\Anaconda3'
isloaded: 1
Maybe I am doing something wrong?

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Accepted Answer

David Garrison
David Garrison on 27 Aug 2020
Beginning in MATLAB R2018b, Python functions that accept numpy arrays may also accept MATLAB arrays without explicit conversion. When necessary, a numpy array can be created explicitly from a MATLAB array. For example, if you have a supported version of Python that is installed with the numpy library, you can do the following:
>> x = rand(2,2); % MATLAB array
>> y = py.numpy.array(x); % numpy array
y =
Python ndarray:
0.5943 0.8064
0.6133 0.1372
Use details function to view the properties of the Python object.
Use double function to convert to a MATLAB array.
Also beginning in MATLAB R2018b, it is possible to convert numeric numpy arrays returned from Python into MATLAB arrays. For example:
>> y = py.numpy.random.random([int32(2), int32(2)]) % numpy array
y =
Python ndarray:
0.5943 0.8064
0.6133 0.1372
Use details function to view the properties of the Python object.
Use double function to convert to a MATLAB array.
>> x = 2*double(y) % MATLAB array
x =
1.1885 1.6129
1.2266 0.2744
See the MATLAB documentation on Passing Matrices and Multidimensional Arrays for additional Information.

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More Answers (4)

Prashanth Ramesh
Prashanth Ramesh on 5 Nov 2018
Please note that MATLAB does not support Anaconda Python. To call Python libraries from MATLAB, you need to install a supported version of the reference implementation (CPython) for Python. MATLAB supports versions 2.7, 3.5, and 3.6. You can download CPython from https://www.python.org/downloads/
However possible workarounds for using Anaconda Python are listed below (though not officially supported):
1. Launch MATLAB from a properly configured Anaconda prompt. Then import numpy.
2. In Anaconda installation directory, copy the files %env_root%/libraries/bin/mkl_* to %env_root%/lib/site-packages/numpy/core.

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Paul Kuberry
Paul Kuberry on 26 Mar 2020
Nicholos already mentioned that the first suggestion worked for him. I want to post an update on the second option.
2. In Anaconda installation directory, copy the files %env_root%/libraries/bin/mkl_* to %env_root%/lib/site-packages/numpy/core.
Recent versions of Anaconda install these files into %env_root%/Library/bin/mkl_* rather than %env_root%/libraries/bin/mkl_*
This is a one-time fix, and allows you to call MATLAB in your own traditional way (from a GUI shortcut, for instance).
Thanks Prashanth for the solution.
krishna maganti
krishna maganti on 10 Apr 2020
Worked on my MAC. Created a virtual env and then ran matlab from the env and set path and run. Done.
Thank you very much.
Seth Wagenman
Seth Wagenman on 31 Aug 2020
Nicholas Richmond if I launch MATLAB from python do I get the normal GUI or just the engine/interpreter?

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Vaibhav Arora
Vaibhav Arora on 6 Apr 2019
Install Python (Cpython) from python.org/downloads.
Make sure the version you download is 64-bit if your Matlab exe is 64-bit. By default, a 32-bit cersion of python is downloaded so be careful.
Open python and try the command "import numpy as np". If you get an error, you need to install the library. For this, go to command prompt and type (for python 3): "pip3 install numpy"
Now you will be able to use numpy library in matlab

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Igor Varfolomeev
Igor Varfolomeev on 9 Apr 2020
Edited: Igor Varfolomeev on 9 Apr 2020
I've noticed that simply adding the folder with the DLLs, related to numpy to PATH, just before starting Python also fixes the issue (R2019b update 5, Windows 10 version 1803).
For example, I create the environment with
conda create -n test_py36 python=3.6 numpy
and use setenv like this:
username = getenv('username');
setenv('PYTHONUNBUFFERED','1'); % doesn't change much, but just-in-case
setenv('path',['C:\Users\' username '\Anaconda3\envs\test_py36\Library\bin;', getenv('path')]);
pe=pyenv('Version',['C:\Users\' username '\Anaconda3\envs\test_py36\pythonw.exe'],...
...'ExecutionMode','OutOfProcess'... --- this (new mode) causes misc. issues
'ExecutionMode','InProcess'... --- this (old mode) works OK
);
py.importlib.import_module('numpy')
(inspired by this)

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Christopher Wingard
Christopher Wingard on 17 Jun 2020
This worked for me. No messing around with copying directories or changing the way I launch Matlab.
Binxu
Binxu on 8 Oct 2020
This works like a charm for me!!! No need to copy paste directories!

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I am not a robot
I am not a robot on 9 Sep 2019
If you have setup an env(-ironment) in Anaconda, you need to setup the pyversion command to use the env.
Adapt the below to suit your needs
pyversion('C:\Users\Your_User_Name\AppData\Local\Continuum\anaconda3\envs\Your_Env\pythonw.exe')

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Bram ter Huurne
Bram ter Huurne on 21 Feb 2020
This generally does not work.
Paul Kuberry
Paul Kuberry on 26 Mar 2020
After doing the above command, you would be left with the same problem as the OP.
The issue is mkl_ libraries not being where they can be found through MATLAB. Prashanth Ramesh's solution resolves this.
Seth Wagenman
Seth Wagenman on 31 Aug 2020
This works generally, Bram ter Huurne:
P.S. Where is the "general matlab-python website" where you suggest posting solutions, "as Anaconda is the general python distribution software for most users?"

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