Indexing array of symbolic variables dependent on time

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Morten Nissov
Morten Nissov 2020-7-16
评论： Walter Roberson 2020-7-16
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)]

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回答（1 个）

Walter Roberson
Walter Roberson 2020-7-16
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.
  2 个评论
Morten Nissov
Morten Nissov 2020-7-16
Is it possible to generate a cell array containing a variable number of symbolic variables? Equivalent to syms x [1,N] but with a cell array instead of array.
Walter Roberson
Walter Roberson 2020-7-16
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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