Subscripting into an mxArray

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?

Answer 1

[Mike Hosea]

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

[Rod]

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]

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

[Sharan Duggirala]

Hi,

During code generation, I keep getting the error -

' CODER.VARSIZE is not applicable to 'mxArray '. '

Has anyone encountered this/ know a way around this?

Here is a screenshot of the code generation error report :

[zeng xiao]

您好哦，您的问题解决了吗？我也遇到了相同的问题，您可以顺便为我解答一下吗？

[gaoliming gao]

Initialize the variable before use it, for example y = zeros(4,1);