Indexing array of symbolic variables dependent on time

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Morten Nissov
Morten Nissov on 16 Jul 2020
Commented: Walter Roberson on 16 Jul 2020
I need to create variable number of symbolic variables and access each of them individually. It is necessary that they are time varying for purposes of calling diff.
So far I can see that a variable number can be created by
N = 5 % number of variables for example
syms x(t) [1,N]
But if one then tries to access the first element, x1(t), this results in
>> x(1)
ans =
[ x1(1), x2(1)]

Answers (1)

Walter Roberson
Walter Roberson on 16 Jul 2020
you cannot do that with the symbolic toolbox. The () indexing is incompatible between symfun and arrays.
If you need an array of symfun then it must be cell array.
Walter Roberson
Walter Roberson on 16 Jul 2020
x = str2sym(compose("x" + (1:4) + "(t)"))
This will be an array of symbols that live at the MuPAD level, and can be operated like
dsolve(diff(x(1),t) == t^2)
but they will not act like symbolic functions. For example if you had done
syms y(t)
then you could use y(0) to represent y evaluated at 0, but you cannot use x(1)(0) and would instead need to use subs(x(1),t,0)

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