array of symbolic variables which are function of time

8 次查看（过去 30 天）
Jai Tushar
Jai Tushar 2017-10-25
编辑： Juraj Lieskovský 2021-3-4
p = sym('p', [m 1]);
the above code gives me an array of symbolic variables, where m is the size of the matrix. However i want to create an array of symbolic variables which are function of time i.e. p1(t),p2(t),.... .

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2017-10-26
There is no facility to do this. You will need to loop (or equivalent). For example in R2017b or later,
p = arrayfun(@(N) str2sym(sprintf('p%d(t)',N)), 1:5).'
  3 个评论
显示 1更早的评论
Walter Roberson
Walter Roberson 2017-10-26
ptemp = arrayfun(@(N) sym(sprintf('p%d(t)',N)), (1:m).', 'uniform', 0);
p = vertcat(ptemp{:});
You might get m warnings along the line of
Warning: Support of character vectors that are not valid variable names or define a number will be removed in a future release. To create symbolic
expressions, first create symbolic variables and then use operations on them.
Jai Tushar
Jai Tushar 2017-10-28
编辑：Jai Tushar 2017-10-28
it worked!!
what does uniform and 0 do in the code?
Also,
ptemp = arrayfun(@(N) sym(sprintf('p%d(t)',N)), (1:2), 'uniform', 0); p = vertcat(ptemp{:});
A = [1 2; -1 1]; odes = diff(p) == A*p
Gives me the output as
odes =
diff(p1(t), t) == p1(t) + 2*p2(t)
diff(p2(t), t) == p2(t) - p1(t)
Why is odes not the funtion of time in the output. When i define p1(t),... and so on manually and define P = [p1; p2] then odes == diff(P) = A*p gives odes as a function of time i.e. odes(t) in the output. W

请先登录，再进行评论。

更多回答（2 个）

Juraj Lieskovský
编辑：Juraj Lieskovský 2021-3-4
Simple solution (using R2020b)
syms t
syms p(t) [m,1]
KSSV
KSSV 2017-10-26
syms p1(t) p2(t) p3(t)
p = [p1 p2 p3]
  1 个评论
Jai Tushar
Jai Tushar 2017-10-26
编辑：Jai Tushar 2017-10-26
you are defining p1(t),... manually here.
I want my script to define them according to the size of the square matrix i enter. For example if i have a (user input) nxn matrix, then the script should define n such symbolic variables which are functions of time.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Numeric Solvers 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by