symbolic variable not recognized

Hi MATLAB world!

I have a weird problem. I have defined 4 symbolic variables (kL, kR, kTR, kTL) for my code. I use these variables in different matrices and find their determinants with no problem.

I then have defined another variable in which I do a algebraic symbolic expression (by that I mean it includes few multiplications and additions and powers)and all of a sudden it does not recognize these variables. I have a variable lambda in there as well and it has no problem with that.

here is the error I get:

Undefined function or variable 'k'.

Error in Eoperator (line 169)

if I define k as a symbol, then it ruins my calculation but does not solve the problem either, it tells me that TL and TR and L and R are undefined.

What am I supposed to do?

Thank you all for your time and help in advance.

[madhan ravi]

Upload your code.

[Stephen23]

*Mohammad Moeid Elahikahooker's "Answer" moved here and formatted properly:

syms lambda
syms L
syms wzero
syms wL
syms phizero
syms phiL
syms wprimezero
syms wdoubleprimezero
syms wtripleprimezero

syms kL
syms kTL
syms kR
syms kTR 

Czero=sym(zeros(4));
Czero(1,1)=cosh(lambda*L)/2;
Czero(1,2)=sinh(lambda*L)/(2*lambda);
Czero(1,3)=cosh(lambda*L)/(2*lambda*lambda);
Czero(1,4)=sinh(lambda*L)/(2*lambda*lambda*lambda);
Czero(2,1)=sinh(lambda*L)/2;
Czero(2,2)=cosh(lambda*L)/(2*lambda);
Czero(2,3)=sinh(lambda*L)/(2*lambda*lambda);
Czero(2,4)=cosh(lambda*L)/(2*lambda*lambda*lambda);
Czero(3,1)=cos(lambda*L)/2;
Czero(3,2)=sin(lambda*L)/(2*lambda);
Czero(3,3)=-1*cos(lambda*L)/(2*lambda*lambda);
Czero(3,4)=-1*sin(lambda*L)/(2*lambda*lambda*lambda);
Czero(4,1)=-1*sin(lambda*L)/2;
Czero(4,2)=cos(lambda*L)/(2*lambda);
Czero(4,3)=sin(lambda*L)/(2*lambda*lambda);
Czero(4,4)=-1*cos(lambda*L)/(2*lambda*lambda*lambda);

CL=sym(zeros(4));
CL(1,1)=1/2;
CL(1,2)=0;
CL(1,3)=1/(2*lambda*lambda);
CL(1,4)=0;
CL(2,1)=0;
CL(2,2)=1/(2*lambda);
CL(2,3)=0;
CL(2,4)=1/(2*lambda*lambda*lambda);
CL(3,1)=1/2;
CL(3,2)=0;
CL(3,3)=-1/(2*lambda*lambda);
CL(3,4)=0;
CL(4,1)=0;
CL(4,2)=1/(2*lambda);
CL(4,3)=0;
CL(4,4)=-1/(2*lambda*lambda*lambda);

% % % %  K_e check

Check2=sym(zeros(4));
Check3=sym(zeros(4));
Check4=sym(zeros(4));
Check5=sym(zeros(4));
Check6=sym(zeros(4));

Check2(:,1)=Czero(:,1);
Check2(:,2)=Czero(:,2);
Check2(:,3)=-CL(:,1);
Check2(:,4)=-CL(:,2);
Check3(:,1)=-Czero(:,4);
Check3(:,2)=-Czero(:,3);
Check3(:,3)=CL(:,4);
Check3(:,4)=CL(:,3);
Check5=inv(Check3)*Check2;
Check6=Check5;
Check6(2,:)=-Check5(2,:);
Check6(3,:)=-Check5(3,:);
Check4=Check6-transpose(Check6)
simplify(Check4,'IgnoreAnalyticConstraints',true)
% % % % % % % % % % % % % % 

BCheck2=sym(zeros(4));
BCheck3=sym(zeros(4));
BCheck4=sym(zeros(4));
BCheck5=sym(zeros(4));
BCheck6=sym(zeros(4));

Bzero=sym(zeros(4));
Bzero(1,1)=-kL*sinh(lambda*L)/(2*lambda*lambda*lambda);
Bzero(1,2)=kTL*cosh(lambda*L)/(2*lambda*lambda);
Bzero(1,3)=0;
Bzero(1,4)=0;
Bzero(2,1)=-kL*cosh(lambda*L)/(2*lambda*lambda*lambda);
Bzero(2,2)=kTL*sinh(lambda*L)/(2*lambda*lambda);
Bzero(2,3)=0;
Bzero(2,4)=0;
Bzero(3,1)=kL*sin(lambda*L)/(2*lambda*lambda*lambda);
Bzero(3,2)=-kTL*cos(lambda*L)/(2*lambda*lambda);
Bzero(3,3)=0;
Bzero(3,4)=0;
Bzero(4,1)=kL*cos(lambda*L)/(2*lambda*lambda*lambda);
Bzero(4,2)=kTL*sin(lambda*L)/(2*lambda*lambda);
Bzero(4,3)=0;
Bzero(4,4)=0;

% % % % % % 

BCheck2(:,1)=Czero(:,1)+Bzero(:,1);
BCheck2(:,2)=Czero(:,2)+Bzero(:,2);
BCheck2(:,3)=-CL(:,1);
BCheck2(:,4)=-CL(:,2);
BCheck3(:,1)=-Czero(:,4)-Bzero(:,4);
BCheck3(:,2)=-Czero(:,3)-Bzero(:,3);
BCheck3(:,3)=CL(:,4);
BCheck3(:,4)=CL(:,3);
BCheck5=inv(BCheck3)*BCheck2
BCheck6=BCheck5;
BCheck6(2,:)=-BCheck5(2,:);
BCheck6(3,:)=-BCheck5(3,:);
BCheck4=BCheck6-transpose(Check6)
simplify(BCheck4,'IgnoreAnalyticConstraints',true)

% % % % % % % % 

% % Bzero=sym(zeros(4));
% % 
% % Bzero(1,3)=-kR*sinh(lambda*L)/(2*lambda*lambda*lambda);
% % Bzero(1,4)=kTR *cosh(lambda*L)/(2*lambda*lambda);
% % 
% % 
% % Bzero(2,3)=-kR*cosh(lambda*L)/(2*lambda*lambda*lambda);
% % Bzero(2,4)=kTR *sinh(lambda*L)/(2*lambda*lambda);
% % 
% % 
% % Bzero(3,3)=kR*sin(lambda*L)/(2*lambda*lambda*lambda);
% % Bzero(3,4)=-kTR *cos(lambda*L)/(2*lambda*lambda);
% % 
% % 
% % Bzero(4,3)=kR*cos(lambda*L)/(2*lambda*lambda*lambda);
% % Bzero(4,4)=kTR *sin(lambda*L)/(2*lambda*lambda);
% % 
% % Bzero
% % 
% % B2Check2(:,1)=Czero(:,1)+Bzero(:,1);
% % B2Check2(:,2)=Czero(:,2)+Bzero(:,2);
% % B2Check2(:,3)=-CL(:,1);
% % B2Check2(:,4)=-CL(:,2);
% % B2Check3(:,1)=-Czero(:,4)-Bzero(:,4);
% % B2Check3(:,2)=-Czero(:,3)-Bzero(:,3);
% % B2Check3(:,3)=CL(:,4);
% % B2Check3(:,4)=CL(:,3);
% % B2Check5=inv(B2Check3)*B2Check2
% % B2Check6=B2Check5;
% % B2Check6(2,:)=-B2Check5(2,:);
% % B2Check6(3,:)=-B2Check5(3,:);
% % B2Check4=B2Check6-transpose(Check6)
% % simplify(B2Check4,'IgnoreAnalyticConstraints',true)
% % 

trial=[0 0 0 0; 0 0 0 0; 0 0 -kR 0; 0 0 0 kTR ];

BL=[0,0,0,kTR /(2*lambda^2); 0,0,-kR/(2*lambda^3),0; 0,0,0,-kTR /(2*lambda^2); 0,0,kR/(2*lambda^3),0];

BBCheck=BCheck6+[0 0 0 0; 0 0 0 0; 0 0 kR 0; 0 0 0 kTR ];

det_BBCheck=simplify(det(BBCheck),'IgnoreAnalyticConstraints',true)

syms paper_det
paper_det=((lambda^4)+kL*kTL)*((lambda^4)+kR*kTR )-2*(lambda^2)*((lambda^4)*kTR *kTL-kL*kR)*sinh(lambda)*sin(lambda)...
    +(2*lambda^4*(kL*kTR +kR*kTL)-(lambda^4-kL*k*TL)*(lambda^4-kR*kTR ))*cosh(lambda)*cos(lambda)...
    -lambda*((lambda^4-kL*kTL)*(lambda^2*kTR +kR)+(lambda^4-kR*kTR )*(lambda^2*kTL+kL))*sin(lambda)*cosh(lambda)...
    -lambda*((lambda^4-kL*kTL)*(lambda^2*kTR -kR)+(lambda^4-kR*kTR )*(lambda^2*kTL-kL))*cos(lambda)*sinh(lambda)

[Stephen23]

"Undefined function or variable 'k'."

Because you don't define any variable k.

"if I define k as a symbol, then it ruins my calculation but does not solve the problem either, it tells me that TL and TR and L and R are undefined."

"What am I supposed to do?"

Don't try to use variables that you have not defined.

It sounds like you expect MATLAB to somehow decompose kTL, etc, into k*TL, or something like that. This is not how symbolic manipulations work. If you want a variable k and a variable TL, then that is what you have to specify.

[Mohammad Moeid Elahikahooker]

Hi Stephen,

Sorry for the confusion, this is actually my second iteration of the code. I tried to remove the underscore from my variables in hopes that it will help.

So I redefined k_L as kL for example and used that.

As you can see in the code, I have defined all the variables I am using and I am still getting the error.

[Torsten]

And what's the error message now ?

Answer 1

[Stephan]

Hi,

look at the second line of paper_det - your code:

lambda^4-kL*k*TL

since there is not k and not TL defined in your code, but kTL is, i would bet, that it should be:

lambda^4-kL*kTL

which is the same structure of the calculation as the other parts of paper_det. Then the code runs without error - so it was just a typo(?)

paper_det=((lambda^4)+kL*kTL)*((lambda^4)+kR*kTR )-2*(lambda^2)*((lambda^4)*kTR *kTL-kL*kR)*sinh(lambda)*sin(lambda)...
    +(2*lambda^4*(kL*kTR +kR*kTL)-(lambda^4-kL*kTL)*(lambda^4-kR*kTR ))*cosh(lambda)*cos(lambda)...
    -lambda*((lambda^4-kL*kTL)*(lambda^2*kTR +kR)+(lambda^4-kR*kTR )*(lambda^2*kTL+kL))*sin(lambda)*cosh(lambda)...
    -lambda*((lambda^4-kL*kTL)*(lambda^2*kTR -kR)+(lambda^4-kR*kTR )*(lambda^2*kTL-kL))*cos(lambda)*sinh(lambda)

Best regards

Stephan

[Mohammad Moeid Elahikahooker]

Thanks Stephan,

days of working on multiple codes in a rush for a paper had blinded me to that mistake.