Error "()-indexing must appear last in an index expression" in symbolic Matlab Toolbox

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paco ocap 2016-8-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/299865-error-indexing-must-appear-last-in-an-index-expression-in-symbolic-matlab-toolbox

编辑： Mischa Kim 2016-8-25

Hello everyone, I want to operate with some symbolic expressions and their derivatives, but I'm finding some problems when trying to do something like this:

>>syms x(t)
>>q=diff(x,t)+2
        q(t) =
        D(x)(t) + 2
>>dq=diff(q,D(x)(t))
        Error: ()-indexing must appear last in an index expression.

I want to differentiate q(t) with respect to the derivative of x(t), and I was wondering if there is any way to do this without substituting D(x)(t) for another variable

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KSSV 2016-8-17

what you want to do actually?

paco ocap 2016-8-17

I want to solve Lagrange equations for any given lagrangian. And as I have many variables, and I dont know which of them is differentiated or not at first, I think it would be easier to solve things following the process showcased in the question. But if it is not possible, I will try to do it another way.

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