Attempting to pass MATLAB arrays into a numpy array

Question

I am trying to call a Matlab function in python via matlab.engine. The function takes one input (a number corresponding to filenum) and ouputs 4 matlab arrays. In the python script I try taking these 4 variables and converting them to a numpy array, however I get an error:

ValueError: too many values to unpack (expected 4)

The original Matlab function line reads as:

function [out1,out2,out3,out4] = myfunc(filenum)

I have tried alternate methods too see why this was happening. Interestingly, if I only store the output of the matlab function in one variable the code works fine, but the variable value is not the one I desire.

Here is all relevant code (other than the matlab function itself):

import matlab.engine
import numpy as np

eng = matlab.engine.start_matlab()

out1,out2,out3,out4 = eng.myfunc(101)

final1 = np.asarray(out1)
final2 = np.asarray(out2)
final3 = np.asarray(out3)
final4 = np.asarray(out4)

Before the final1... code block can even run I get the error on the line where I try calling the function.

Also I am positive the Matlab function works and it does output 4 arrays.

Cris Luengo · Accepted Answer · 2019-05-14 17:38:32Z

1

The documentation says:

If you know that the function can return multiple arguments, use the nargout argument to specify the number of output arguments.

And then it gives an example:

t = eng.gcd(100.0,80.0,nargout=3)
print(t)

(20.0, 1.0, -1.0)

Thus, you probably need to do

out1,out2,out3,out4 = eng.myfunc(101,nargout=4)

answered May 14, 2019 at 17:38

Cris Luengo

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