Matlab Coder does not properly execute/support mldivide (a.k.a "\") ?

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xavier soltner 2021-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/814770-matlab-coder-does-not-properly-execute-support-mldivide-a-k-a

回答： xavier soltner 2021-4-29

采纳的回答： xavier soltner

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Hi,

I'm having trouble with Matlab Coder who seems to not properly execute the mldivide(a,b) function..

The code is supposed to calculate the misplacement of a workpiece position. The part I have trouble with is the following :

% construct vector and matrices, around current estimate of p, to have: dmes=V+M*pest => pest=M\(dmes-V)
                V=d(pest)-pest(1)*dd_dx(pest)-pest(2)*dd_dy(pest)-pest(3)*dd_dtheta(pest);
                M=[dd_dx(pest), dd_dy(pest), dd_dtheta(pest)];
                
                fprintf("V1=%f V2=%f V3=%f\n",V(1),V(2),V(3));
                fprintf("M11=%f M12=%f M13=%f\n",M(1,1),M(1,2),M(1,3));
                fprintf("M21=%f M22=%f M23=%f\n",M(2,1),M(2,2),M(2,3));
                fprintf("M31=%f M32=%f M33=%f\n",M(3,1),M(3,2),M(3,3));
                % resolve for new value of pest
                tempVar=(dmes-V);
                pest=mldivide(M,tempVar);
                %pest=M\(dmes-V);
                fprintf("pest1=%f pest2=%f pest3=%f\n",pest(1),pest(2),pest(3));

When directly executing the code with Matlab I have the following output:

dmes1=0.000250 dmes2=-0.000360 dmes3=0.000156
V1=0.000000 V2=0.000000 V3=0.000000
M11=-0.707107 M12=0.707107 M13=19.996980
M21=-0.707107 M22=-0.707107 M23=19.996980
M31=1.000000 M32=0.000000 M33=20.000000
%execution of mldivide in matlab
pest1=0.000124 pest2=0.000431 pest3=0.000002 

Wich give me the correct pest(=PositionEstimation) of the workpiece, but when I execute it in my C++ program I have the following :

dmes1=0.000250 dmes2=-0.000360 dmes3=0.000156
V1=0.000000 V2=0.000000 V3=0.000000
M11=-0.707107 M12=0.707107 M13=19.996980
M21=-0.707107 M22=-0.707107 M23=19.996980
M31=1.000000 M32=0.000000 M33=20.000000
%execution of mldivide in C++ programm
pest1=nan pest2=nan pest3=nan

Anyone know the reason for this to happen or any fix ?

Regards,

Xavier

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Ji Lee 2021-4-28

It seems like there is some amount of code missing from the snippet posted. Namely, the variables used on the first line of code (right-hand side of the assignment into V) look undefined. Would you be able to fill in the missing gap(s)?

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Answer 1

xavier soltner 2021-4-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/814770-matlab-coder-does-not-properly-execute-support-mldivide-a-k-a#answer_687640

Ok I find out the problem : mldivide(A,B) does not support the input if A or B contain NaN value, wich I didn't know..

When I was doing my test in Matlab, my input variable (A and B) was completely defined with value, wich was not the case when I was compiling with the Coder where A and B was of size (500,3) with undefined value in it...

Maybe I should read the documentation more carefully the next time...