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Call poly2trellis in Python

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blue_sdr
blue_sdr on 23 Feb 2017
Commented: blue_sdr on 27 Feb 2017
Hi!
I want to call 'poly2trellis' from Python:
my_trellis = eng.poly2trellis(7, [133, 171])
This results in the following error:
Error using commstr2poly (line 180) Input must be a character vector or a cell of character vectors.
Error in poly2trellis (line 42) cellOutput = commstr2poly(codeGenerator, 'octal');
Thus, I did
function [ trellis ] = get_trellis( )
trellis = poly2trellis(7, [133 171]);
end
It works with all I want to do, but obviously I lost the ability to parameterize it. This is my next approach:
function [ trellis ] = get_trellis( L_C )
trellis = poly2trellis(L_C, [133 171]);
end
This is called in Python with:
eng.get_trellis(7)
And it stops working with:
Error using poly2trellis_mex Input arguments must be nonempty real matrices.
Error in poly2trellis (line 51) trellis = poly2trellis_mex(varargin{:});
Error in get_trellis (line 4) trellis = poly2trellis(L_C, [133 171]);
The same function works if I call it in Matlab directly, but here I need MEfP, so this is not an option. Furthermore, I want to call 'poly2trellis' directly.
Any ideas how to make this work?
Thanks!

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Accepted Answer

Bo Li
Bo Li on 27 Feb 2017
You need to use mlArray in order to pass an array to MATLAB from Python. A Python list is converted into a MATLAB Cell array which is not accepted by "poly2trellis". Try this:
>>> eng.poly2trellis(7.0, matlab.double([133,171]))
Reference:

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blue_sdr
blue_sdr on 27 Feb 2017
Thanks! It works!

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More Answers (3)

Image Analyst
Image Analyst on 23 Feb 2017
It seems to be saying you called it without passing in anything for L_C
trellis = get_trellis();
Is that what you did? If so you'll need to pass in 7 or something
trellis = get_trellis(7);

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blue_sdr
blue_sdr on 24 Feb 2017
I started with the first version without any arguments. This version works. But the second version with one argument does not work. It does not fail because of a missing argument, but because
Error in get_trellis (line 4) trellis = poly2trellis(L_C, [133 171]);
and I called it with
eng.get_trellis(7)
Also, it works in Matlab, but the MEfP call fails.

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Bo Li
Bo Li on 24 Feb 2017
How about trying following:
>>>eng.get_trellis(7.0)
It looks that the poly2trellis expects the first argument to be a double, but Python Engine convert 7 to int64:
In MATLAB, a number is by default "double" type. If you do following in MATLAB, you can the see the same error:
>> trellis = poly2trellis(int64(7), [133 171]);
Error using poly2trellis_mex
Input arguments must be nonempty real matrices.
Error in poly2trellis (line 51)
trellis = poly2trellis_mex(varargin{:});

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blue_sdr
blue_sdr on 27 Feb 2017
Thanks for the suggestions so far.
I modified my code
function [ trellis ] = get_trellis( lc )
lc = double(lc);
poly = [133 171];
trellis = poly2trellis(lc, poly);
end
Now, in MEfP, the call 'eng.get_trellis(7)' works.
Further, I want to 'poly' to be a parameter. I modified my function like this:
function [ trellis ] = get_trellis( lc, poly )
lc = double(lc);
if iscell(poly)
poly = cell2mat(poly);
poly = double(poly);
end
trellis = poly2trellis(lc, poly);
end
Now, this works too. with 'eng.get_trellis(7, [133, 171])'. This is something that really surprises me, because I tested it before and it failed on me.
Finally, I want to call 'poly2trellis' directly.
eng.poly2trellis(7.0, [133.0, 171.0])
This last one does not work. The error messages is as follows.
Error using commstr2poly (line 180) Input must be a character vector or a cell of character vectors.
Error in poly2trellis (line 42) cellOutput = commstr2poly(codeGenerator, 'octal');
How can I make the last call to 'poly2trellis' work?

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