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pythonmatlab
Carnez Davis
Carnez Davis

Reputation: 863

Sprintf MATLAB and Python

I am trying to pass a matrix variable from MATLAB to python, but I am only acquiring the first element of that matrix in python. Does anyone know can get the full matrix?

Python

import sys


if __name__ == '__main__':
    x = sys.argv[1]
    print x

MATLAB

A = magic(5);
[str,err] = sprintf('/usr/local/python name_of_program.py %d ', A);
unix(str)

Upvotes: 3

Views: 974

Answers (2)

munk
munk

Reputation: 12983

You might want to use numpy to reshape the array, too. Or if it's too much to import, you could make your own reshape function Try this:

import sys, numpy
if __name__ == '__main__':
    x = sys.argv[1::3]
    y = numpy.reshape(x, (5,5))
    print y

I also notice that the call is adding the string once for each element of A, so you might consider using mat2str(A), like:

[str, err] = sprintf('/usr/local/python program.py "%s" ', mat2str(A));

I've also changed the %d to %s, because you're passing it as a string on the python anyway. The output of this is:

python program.py "[17 24 1 8 15;23 5 7 14 16;4 6 13 20 22;10 12 19 21 3;11 18 25 2 9]"

You can make a matrix from that string with numpy as well

>>> import sys
>>> import numpy

>>> print(numpy.matrix(sys.argv[1]))

matrix([[17, 24,  1,  8, 15],
    [23,  5,  7, 14, 16],
    [ 4,  6, 13, 20, 22],
    [10, 12, 19, 21,  3],
    [11, 18, 25,  2,  9]])

Upvotes: 0

Joseph Stine
Joseph Stine

Reputation: 1022

Look at the contents of str: /usr/local/python name_of_program.py 17 /usr/local/python name_of_program.py 23 /usr/local/python name_of_program.py 4 ...

When you pass a 5x5 matrix to sprintf, it reproduce the formatting string 25 times, with one of the elements substituted for the %d, in order (column by column).

I suggest another way to transfer data between the programs, such as writing it to a file. If you really want to pass everything on the command line, try the following:

A_str = sprintf(' %d',A);
str = strcat('/usr/local/python name_of_program.py ',A_str);

Upvotes: 1

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