MATLAB: Symbolic variable not recognized

symbolicvariable

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.

Best Answer

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
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