Call poly2trellis in Python

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!

Answer 1

[Bo Li]

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:

http://www.mathworks.com/help/matlab/matlab_external/use-matlab-arrays-in-python.html

[blue_sdr]

Thanks! It works!

Answer 2

[Image Analyst]

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);

[blue_sdr]

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.

Answer 3

[Bo Li]

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:

http://www.mathworks.com/help/matlab/matlab_external/pass-data-to-matlab-from-python.html

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{:});

Answer 4

[blue_sdr]

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?