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Subscripting into an mxArray

Asked by ECE09 ITBHU on 8 Aug 2011

given below is a part of the code i am writing for kalman filter but got error while converting from .m to .c/.c++

>> white_gauss=wgn(1,37000,20); q1=cov(white_gauss); q2=cov(white_gauss); q3=cov(white_gauss);

 loop_count=12; 
L=loop_count; 
Q=[q1(L) q2(L) q3(L)] >>>
 and got following error while converting from .m to .c using matlab coder.

"Subscripting into an mxArray is not supported. "

>>how to avoid it?

0 Comments

ECE09 ITBHU

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1 Answer

Answer by Mike Hosea on 9 Aug 2011
Accepted answer

That is the error you get when you use coder.extrinsic and fail to declare the output before calling the extrinsic function. If you only want to pass the output to extrinsic functions, you don't have to, but if you want to index into the result, you have to pre-define its size and type. For example, suppose foo(x) returns a result with the same size and type as x. Then you could write

y = x;
y = foo(x);

Or if foo always returns a 4-by-1 array of int32's, you would write

y = zeros(4,1,'int32');
y = foo(x);

This tells the compiler how to deconstruct the data structure that comes back from MATLAB when the function foo is called with x as input. -- Mike

2 Comments

Rod on 16 Aug 2013

Hi, I'm having a similar problem calling the poyxpoly as extrinsic in a matlab function block in simulink.

My problem is that the output of this function is an x by 2 array, with x varying. I am therefore unable to index (an use) the output.

Would you know a way around this?

Jan Simon on 17 Aug 2013

@Rod: Please post a new question in a new thread, and not as comment to an answer of a similar question.

Mike Hosea

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